[PATCH v5 00/21] AMX Support in KVM

[PATCH v5 00/21] AMX Support in KVM

[Yang Zhong]

Thanks a lot for all the review comments and guidance! Hope this
version is in a good state now. :)

(Jing is temporarily leave for family reason, Yang helped work out
this version)

----
v4->v5:
  - Directly call fpu core to expand fpstate buffer in kvm_check_cpuid()
    and remove duplicated permission check there (Sean)
  - Accordingly remove Thomas's reviewed-by as a different wrapper is
    introduced now (patch-7)
  - Properly queue #NM exception in nested scenario (Sean)
  - Verify non-XFD related #NM usage in nested scenario (Sean)
  - Hide XFD in kvm_cpu_cap on 32bit host kernels (Sean)
  - Use xstate_required_size() in KVM_CAP_XSAVE2 which may be called
    before any vcpu is created (Sean/Paolo)
  - Replace boot_cpu_has with kvm_cpu_cap_has when disabling RDMSR
    interception for xfd_err (Sean)

v3->v4:
  - Verify kvm selftest for AMX (Paolo)
  - Expand fpstate buffer in kvm_check_cpuid() and improve patch
    description (Sean)
  - Drop 'preemption' word in #NM interception patch (Sean)
  - Remove 'trap_nm' flag. Replace it by: (Sean)
    * Trapping #NM according to guest_fpu::xfd when write to xfd is
      intercepted.
    * Always trapping #NM when xfd write interception is disabled
  - Use better name for #NM related functions (Sean)
  - Drop '#ifdef CONFIG_X86_64' in __kvm_set_xcr (Sean)
  - Update description for KVM_CAP_XSAVE2 and prevent the guest from
    using the wrong ioctl (Sean)
  - Replace 'xfd_out_of_sync' with a better name (Sean)

v2->v3:
  - Trap #NM until write IA32_XFD with a non-zero value (Thomas)
  - Revise return value in __xstate_request_perm() (Thomas)
  - Revise doc for KVM_GET_SUPPORTED_CPUID (Paolo)
  - Add Thomas's reviewed-by on one patch
  - Reorder disabling read interception of XFD_ERR patch (Paolo)
  - Move disabling r/w interception of XFD from x86.c to vmx.c (Paolo)
  - Provide the API doc together with the new KVM_GET_XSAVE2 ioctl (Paolo)
  - Make KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) return minimum size of struct
    kvm_xsave (4K) (Paolo)
  - Request permission at the start of vm_create_with_vcpus() in selftest
  - Request permission conditionally when XFD is supported (Paolo)

v1->v2:
  - Live migration supported and verified with a selftest
  - Rebase to Thomas's new series for guest fpstate reallocation [1]
  - Expand fpstate at KVM_SET_CPUID2 instead of when emulating XCR0
    and IA32_XFD (Thomas/Paolo)
  - Accordingly remove all exit-to-userspace stuff
  - Intercept #NM to save guest XFD_ERR and restore host/guest value
    at preemption on/off boundary (Thomas)
  - Accordingly remove all xfd_err logic in preemption callback and
    fpu_swap_kvm_fpstate()
  - Reuse KVM_SET_XSAVE to handle both legacy and expanded buffer (Paolo)
  - Don't return dynamic bits w/o prctl() in KVM_GET_SUPPORTED_CPUID (Paolo)
  - Check guest permissions for dynamic features in CPUID[0xD] instead
    of only for AMX at KVM_SET_CPUID (Paolo)
  - Remove dynamic bit check for 32-bit guest in __kvm_set_xcr() (Paolo)
  - Fix CPUID emulation for 0x1d and 0x1e (Paolo)
  - Move "disable interception" to the end of the series (Paolo)

This series brings AMX (Advanced Matrix eXtensions) virtualization support to
KVM. The preparatory series from Thomas [1] is also included. 

A large portion of the changes in this series is to deal with eXtended Feature
Disable (XFD) which allows resizing of the fpstate buffer to support
dynamically-enabled XSTATE features with large state component (e.g. 8K for AMX).

There are a lot of simplications when comparing v5 to the original proposal [2]
and the first version [3]. Thanks to Thomas, Paolo and Sean for many good
suggestions. 

The support is based on following key changes:

  - Guest permissions for dynamically-enabled XSAVE features

    Native tasks have to request permission via prctl() before touching
    a dynamic-resized XSTATE compoenent. Introduce guest permissions 
    for the similar purpose. Userspace VMM is expected to request guest
    permission only once when the first vCPU is created.

    KVM checks guest permission in KVM_SET_CPUID2. Setting XFD in guest
    cpuid w/o proper permissions fails this operation. In the meantime,
    unpermitted features are also excluded in KVM_GET_SUPPORTED_CPUID.

  - Extend fpstate reallocation mechanism to cover guest fpu

    Unlike native tasks which have reallocation triggered from #NM 
    handler, guest fpstate reallocation is requested by KVM when it
    identifies the intention on using dynamically-enabled XSAVE
    features inside guest.

    Extend fpu core to allow KVM request fpstate buffer expansion
    for a guest fpu containter.

  - Trigger fpstate reallocation in KVM

    This could be done either before guest runs or until xfd is updated
    in the emulation path. According to discussion [1] we decide to 
    go the former option in KVM_SET_CPUID2, with fpstate buffer sized
    accordingly. This spares a lot of code and also avoid imposing an
    ordered restore sequence (XCR0, XFD and XSTATE) to userspace VMM.

  - RDMSR/WRMSR emulation for IA32_XFD

    Because fpstate expansion is completed in KVM_SET_CPUID2, emulating
    r/w access to IA32_XFD simply involves the xfd field in the guest 
    fpu container. If write and guest fpu is currently active, the 
    software state (guest_fpstate::xfd and per-cpu xfd cache) is also
    updated.

  - RDMSR/WRMSR emulation for XFD_ERR

    When XFD causes an instruction to generate #NM, XFD_ERR contains
    information about which disabled state components are being accessed.
    It'd be problematic if the XFD_ERR value generated in guest is 
    consumed/clobbered by the host before the guest itself doing so. 

    Intercept #NM exception to save the guest XFD_ERR value when write
    IA32_XFD with a non-zero value for 1st time. There is at most one
    interception per guest task given a dynamic feature.

    RDMSR/WRMSR emulation uses the saved value. The host value (always
    ZERO outside of the host #NM handler) is restored before enabling
    interrupts. The saved guest value is restored right before entering
    the guest (with interrupts disabled).

  - Get/set dynamic xfeature state for migration

    Introduce new capability (KVM_CAP_XSAVE2) to deal with >4KB fpstate
    buffer. Reading this capability returns the size of the current 
    guest fpstate (e.g. after expansion). Userspace VMM uses a new ioctl
    (KVM_GET_XSAVE2) to read guest fpstate from the kernel and reuses
    the existing ioctl (KVM_SET_XSAVE) to update guest fpsate to the
    kernel. KVM_SET_XSAVE is extended to do properly_sized memdup_user()
    based on the guest fpstate.

  - Expose related cpuid bits to guest

    The last step is to allow exposing XFD, AMX_TILE, AMX_INT8 and
    AMX_BF16 in guest cpuid. Adding those bits into kvm_cpu_caps finally
    activates all previous logics in this series

  - Optimization: disable interception for IA32_XFD

    IA32_XFD can be frequently updated by the guest, as it is part of
    the task state and swapped in context switch when prev and next have
    different XFD setting. Always intercepting WRMSR can easily cause
    non-negligible overhead.

    Disable r/w emulation for IA32_XFD after intercepting the first
    WRMSR(IA32_XFD) with a non-zero value. However MSR passthrough 
    implies the software state (guest_fpstate::xfd and per-cpu xfd
    cache) might be out of sync with MSR. This suggests KVM needs to
    re-sync them at VM-exit before preemption is enabled.

Thanks Jun Nakajima and Kevin Tian for the design suggestions when this was
being internally worked on.

[1] https://lore.kernel.org/all/20211214022825.563892248@linutronix.de/
[2] https://www.spinics.net/lists/kvm/msg259015.html
[3] https://lore.kernel.org/lkml/20211208000359.2853257-1-yang.zhong@intel.com/

Thanks,
Yang
----

Guang Zeng (1):
  kvm: x86: Add support for getting/setting expanded xstate buffer

Jing Liu (11):
  kvm: x86: Fix xstate_required_size() to follow XSTATE alignment rule
  kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID
  x86/fpu: Make XFD initialization in __fpstate_reset() a function
    argument
  kvm: x86: Enable dynamic xfeatures at KVM_SET_CPUID2
  kvm: x86: Add emulation for IA32_XFD
  x86/fpu: Prepare xfd_err in struct fpu_guest
  kvm: x86: Intercept #NM for saving IA32_XFD_ERR
  kvm: x86: Emulate IA32_XFD_ERR for guest
  kvm: x86: Disable RDMSR interception of IA32_XFD_ERR
  kvm: x86: Add XCR0 support for Intel AMX
  kvm: x86: Add CPUID support for Intel AMX

Kevin Tian (2):
  x86/fpu: Provide fpu_update_guest_xfd() for IA32_XFD emulation
  kvm: x86: Disable interception for IA32_XFD on demand

Sean Christopherson (1):
  x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM

Thomas Gleixner (5):
  x86/fpu: Extend fpu_xstate_prctl() with guest permissions
  x86/fpu: Prepare guest FPU for dynamically enabled FPU features
  x86/fpu: Add guest support to xfd_enable_feature()
  x86/fpu: Add uabi_size to guest_fpu
  x86/fpu: Provide fpu_sync_guest_vmexit_xfd_state()

Wei Wang (1):
  kvm: selftests: Add support for KVM_CAP_XSAVE2

 Documentation/virt/kvm/api.rst                |  46 +++++-
 arch/x86/include/asm/cpufeatures.h            |   2 +
 arch/x86/include/asm/fpu/api.h                |  11 ++
 arch/x86/include/asm/fpu/types.h              |  32 ++++
 arch/x86/include/asm/kvm_host.h               |   1 +
 arch/x86/include/uapi/asm/kvm.h               |  16 +-
 arch/x86/include/uapi/asm/prctl.h             |  26 ++--
 arch/x86/kernel/fpu/core.c                    |  94 ++++++++++-
 arch/x86/kernel/fpu/xstate.c                  | 147 +++++++++++-------
 arch/x86/kernel/fpu/xstate.h                  |  15 +-
 arch/x86/kernel/process.c                     |   2 +
 arch/x86/kvm/cpuid.c                          |  86 +++++++---
 arch/x86/kvm/cpuid.h                          |   2 +
 arch/x86/kvm/vmx/vmcs.h                       |   5 +
 arch/x86/kvm/vmx/vmx.c                        |  68 ++++++++
 arch/x86/kvm/vmx/vmx.h                        |   2 +-
 arch/x86/kvm/x86.c                            | 112 ++++++++++++-
 include/uapi/linux/kvm.h                      |   4 +
 tools/arch/x86/include/uapi/asm/kvm.h         |  16 +-
 tools/include/uapi/linux/kvm.h                |   3 +
 .../testing/selftests/kvm/include/kvm_util.h  |   2 +
 .../selftests/kvm/include/x86_64/processor.h  |  10 ++
 tools/testing/selftests/kvm/lib/kvm_util.c    |  32 ++++
 .../selftests/kvm/lib/x86_64/processor.c      |  67 +++++++-
 .../testing/selftests/kvm/x86_64/evmcs_test.c |   2 +-
 tools/testing/selftests/kvm/x86_64/smm_test.c |   2 +-
 .../testing/selftests/kvm/x86_64/state_test.c |   2 +-
 .../kvm/x86_64/vmx_preemption_timer_test.c    |   2 +-
 28 files changed, 702 insertions(+), 107 deletions(-)

[PATCH v5 01/21] x86/fpu: Extend fpu_xstate_prctl() with guest permissions

[Yang Zhong]

From: Thomas Gleixner <tglx@linutronix.de>

KVM requires a clear separation of host user space and guest permissions
for dynamic XSTATE components.

Add a guest permissions member to struct fpu and a separate set of prctl()
arguments: ARCH_GET_XCOMP_GUEST_PERM and ARCH_REQ_XCOMP_GUEST_PERM.

The semantics are equivalent to the host user space permission control
except for the following constraints:

  1) Permissions have to be requested before the first vCPU is created

  2) Permissions are frozen when the first vCPU is created to ensure
     consistency. Any attempt to expand permissions via the prctl() after
     that point is rejected.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/api.h    |  2 ++
 arch/x86/include/asm/fpu/types.h  |  9 ++++++
 arch/x86/include/uapi/asm/prctl.h | 26 ++++++++-------
 arch/x86/kernel/fpu/core.c        |  3 ++
 arch/x86/kernel/fpu/xstate.c      | 53 +++++++++++++++++++++++--------
 arch/x86/kernel/fpu/xstate.h      | 13 ++++++--
 arch/x86/kernel/process.c         |  2 ++
 7 files changed, 80 insertions(+), 28 deletions(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index c2767a6a387e..d8c222290e68 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -132,6 +132,8 @@ static inline void fpstate_free(struct fpu *fpu) { }
 /* fpstate-related functions which are exported to KVM */
 extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
 
+extern inline u64 xstate_get_guest_group_perm(void);
+
 /* KVM specific functions */
 extern bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu);
 extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 3c06c82ab355..6ddf80637697 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -387,6 +387,8 @@ struct fpstate {
 	/* @regs is dynamically sized! Don't add anything after @regs! */
 } __aligned(64);
 
+#define FPU_GUEST_PERM_LOCKED		BIT_ULL(63)
+
 struct fpu_state_perm {
 	/*
 	 * @__state_perm:
@@ -476,6 +478,13 @@ struct fpu {
 	 */
 	struct fpu_state_perm		perm;
 
+	/*
+	 * @guest_perm:
+	 *
+	 * Permission related information for guest pseudo FPUs
+	 */
+	struct fpu_state_perm		guest_perm;
+
 	/*
 	 * @__fpstate:
 	 *
diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 754a07856817..500b96e71f18 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -2,20 +2,22 @@
 #ifndef _ASM_X86_PRCTL_H
 #define _ASM_X86_PRCTL_H
 
-#define ARCH_SET_GS		0x1001
-#define ARCH_SET_FS		0x1002
-#define ARCH_GET_FS		0x1003
-#define ARCH_GET_GS		0x1004
+#define ARCH_SET_GS			0x1001
+#define ARCH_SET_FS			0x1002
+#define ARCH_GET_FS			0x1003
+#define ARCH_GET_GS			0x1004
 
-#define ARCH_GET_CPUID		0x1011
-#define ARCH_SET_CPUID		0x1012
+#define ARCH_GET_CPUID			0x1011
+#define ARCH_SET_CPUID			0x1012
 
-#define ARCH_GET_XCOMP_SUPP	0x1021
-#define ARCH_GET_XCOMP_PERM	0x1022
-#define ARCH_REQ_XCOMP_PERM	0x1023
+#define ARCH_GET_XCOMP_SUPP		0x1021
+#define ARCH_GET_XCOMP_PERM		0x1022
+#define ARCH_REQ_XCOMP_PERM		0x1023
+#define ARCH_GET_XCOMP_GUEST_PERM	0x1024
+#define ARCH_REQ_XCOMP_GUEST_PERM	0x1025
 
-#define ARCH_MAP_VDSO_X32	0x2001
-#define ARCH_MAP_VDSO_32	0x2002
-#define ARCH_MAP_VDSO_64	0x2003
+#define ARCH_MAP_VDSO_X32		0x2001
+#define ARCH_MAP_VDSO_32		0x2002
+#define ARCH_MAP_VDSO_64		0x2003
 
 #endif /* _ASM_X86_PRCTL_H */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 8ea306b1bf8e..ab19b3d8b2f7 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -450,6 +450,8 @@ void fpstate_reset(struct fpu *fpu)
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;
 	fpu->perm.__state_size		= fpu_kernel_cfg.default_size;
 	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;
+	/* Same defaults for guests */
+	fpu->guest_perm = fpu->perm;
 }
 
 static inline void fpu_inherit_perms(struct fpu *dst_fpu)
@@ -460,6 +462,7 @@ static inline void fpu_inherit_perms(struct fpu *dst_fpu)
 		spin_lock_irq(&current->sighand->siglock);
 		/* Fork also inherits the permissions of the parent */
 		dst_fpu->perm = src_fpu->perm;
+		dst_fpu->guest_perm = src_fpu->guest_perm;
 		spin_unlock_irq(&current->sighand->siglock);
 	}
 }
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index d28829403ed0..5f01d463859d 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1595,7 +1595,7 @@ static int validate_sigaltstack(unsigned int usize)
 	return 0;
 }
 
-static int __xstate_request_perm(u64 permitted, u64 requested)
+static int __xstate_request_perm(u64 permitted, u64 requested, bool guest)
 {
 	/*
 	 * This deliberately does not exclude !XSAVES as we still might
@@ -1605,9 +1605,10 @@ static int __xstate_request_perm(u64 permitted, u64 requested)
 	 */
 	bool compacted = cpu_feature_enabled(X86_FEATURE_XSAVES);
 	struct fpu *fpu = &current->group_leader->thread.fpu;
+	struct fpu_state_perm *perm;
 	unsigned int ksize, usize;
 	u64 mask;
-	int ret;
+	int ret = 0;
 
 	/* Check whether fully enabled */
 	if ((permitted & requested) == requested)
@@ -1621,15 +1622,18 @@ static int __xstate_request_perm(u64 permitted, u64 requested)
 	mask &= XFEATURE_MASK_USER_SUPPORTED;
 	usize = xstate_calculate_size(mask, false);
 
-	ret = validate_sigaltstack(usize);
-	if (ret)
-		return ret;
+	if (!guest) {
+		ret = validate_sigaltstack(usize);
+		if (ret)
+			return ret;
+	}
 
+	perm = guest ? &fpu->guest_perm : &fpu->perm;
 	/* Pairs with the READ_ONCE() in xstate_get_group_perm() */
-	WRITE_ONCE(fpu->perm.__state_perm, requested);
+	WRITE_ONCE(perm->__state_perm, requested);
 	/* Protected by sighand lock */
-	fpu->perm.__state_size = ksize;
-	fpu->perm.__user_state_size = usize;
+	perm->__state_size = ksize;
+	perm->__user_state_size = usize;
 	return ret;
 }
 
@@ -1640,7 +1644,7 @@ static const u64 xstate_prctl_req[XFEATURE_MAX] = {
 	[XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE_DATA,
 };
 
-static int xstate_request_perm(unsigned long idx)
+static int xstate_request_perm(unsigned long idx, bool guest)
 {
 	u64 permitted, requested;
 	int ret;
@@ -1661,14 +1665,19 @@ static int xstate_request_perm(unsigned long idx)
 		return -EOPNOTSUPP;
 
 	/* Lockless quick check */
-	permitted = xstate_get_host_group_perm();
+	permitted = xstate_get_group_perm(guest);
 	if ((permitted & requested) == requested)
 		return 0;
 
 	/* Protect against concurrent modifications */
 	spin_lock_irq(&current->sighand->siglock);
-	permitted = xstate_get_host_group_perm();
-	ret = __xstate_request_perm(permitted, requested);
+	permitted = xstate_get_group_perm(guest);
+
+	/* First vCPU allocation locks the permissions. */
+	if (guest && (permitted & FPU_GUEST_PERM_LOCKED))
+		ret = -EBUSY;
+	else
+		ret = __xstate_request_perm(permitted, requested, guest);
 	spin_unlock_irq(&current->sighand->siglock);
 	return ret;
 }
@@ -1713,12 +1722,18 @@ int xfd_enable_feature(u64 xfd_err)
 	return 0;
 }
 #else /* CONFIG_X86_64 */
-static inline int xstate_request_perm(unsigned long idx)
+static inline int xstate_request_perm(unsigned long idx, bool guest)
 {
 	return -EPERM;
 }
 #endif  /* !CONFIG_X86_64 */
 
+inline u64 xstate_get_guest_group_perm(void)
+{
+	return xstate_get_group_perm(true);
+}
+EXPORT_SYMBOL_GPL(xstate_get_guest_group_perm);
+
 /**
  * fpu_xstate_prctl - xstate permission operations
  * @tsk:	Redundant pointer to current
@@ -1742,6 +1757,7 @@ long fpu_xstate_prctl(struct task_struct *tsk, int option, unsigned long arg2)
 	u64 __user *uptr = (u64 __user *)arg2;
 	u64 permitted, supported;
 	unsigned long idx = arg2;
+	bool guest = false;
 
 	if (tsk != current)
 		return -EPERM;
@@ -1760,11 +1776,20 @@ long fpu_xstate_prctl(struct task_struct *tsk, int option, unsigned long arg2)
 		permitted &= XFEATURE_MASK_USER_SUPPORTED;
 		return put_user(permitted, uptr);
 
+	case ARCH_GET_XCOMP_GUEST_PERM:
+		permitted = xstate_get_guest_group_perm();
+		permitted &= XFEATURE_MASK_USER_SUPPORTED;
+		return put_user(permitted, uptr);
+
+	case ARCH_REQ_XCOMP_GUEST_PERM:
+		guest = true;
+		fallthrough;
+
 	case ARCH_REQ_XCOMP_PERM:
 		if (!IS_ENABLED(CONFIG_X86_64))
 			return -EOPNOTSUPP;
 
-		return xstate_request_perm(idx);
+		return xstate_request_perm(idx, guest);
 
 	default:
 		return -EINVAL;
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 86ea7c0fa2f6..98a472775c97 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -20,10 +20,19 @@ static inline void xstate_init_xcomp_bv(struct xregs_state *xsave, u64 mask)
 		xsave->header.xcomp_bv = mask | XCOMP_BV_COMPACTED_FORMAT;
 }
 
-static inline u64 xstate_get_host_group_perm(void)
+static inline u64 xstate_get_group_perm(bool guest)
 {
+	struct fpu *fpu = &current->group_leader->thread.fpu;
+	struct fpu_state_perm *perm;
+
 	/* Pairs with WRITE_ONCE() in xstate_request_perm() */
-	return READ_ONCE(current->group_leader->thread.fpu.perm.__state_perm);
+	perm = guest ? &fpu->guest_perm : &fpu->perm;
+	return READ_ONCE(perm->__state_perm);
+}
+
+static inline u64 xstate_get_host_group_perm(void)
+{
+	return xstate_get_group_perm(false);
 }
 
 enum xstate_copy_mode {
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 04143a653a8a..d7bc23589062 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -993,6 +993,8 @@ long do_arch_prctl_common(struct task_struct *task, int option,
 	case ARCH_GET_XCOMP_SUPP:
 	case ARCH_GET_XCOMP_PERM:
 	case ARCH_REQ_XCOMP_PERM:
+	case ARCH_GET_XCOMP_GUEST_PERM:
+	case ARCH_REQ_XCOMP_GUEST_PERM:
 		return fpu_xstate_prctl(task, option, arg2);
 	}
 

[PATCH v5 02/21] x86/fpu: Prepare guest FPU for dynamically enabled FPU features

[Yang Zhong]

From: Thomas Gleixner <tglx@linutronix.de>

To support dynamically enabled FPU features for guests prepare the guest
pseudo FPU container to keep track of the currently enabled xfeatures and
the guest permissions.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/types.h | 13 +++++++++++++
 arch/x86/kernel/fpu/core.c       | 26 +++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 6ddf80637697..c752d0aa23a4 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -504,6 +504,19 @@ struct fpu {
  * Guest pseudo FPU container
  */
 struct fpu_guest {
+	/*
+	 * @xfeatures:			xfeature bitmap of features which are
+	 *				currently enabled for the guest vCPU.
+	 */
+	u64				xfeatures;
+
+	/*
+	 * @perm:			xfeature bitmap of features which are
+	 *				permitted to be enabled for the guest
+	 *				vCPU.
+	 */
+	u64				perm;
+
 	/*
 	 * @fpstate:			Pointer to the allocated guest fpstate
 	 */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index ab19b3d8b2f7..eddeeb4ed2f5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -201,6 +201,26 @@ void fpu_reset_from_exception_fixup(void)
 #if IS_ENABLED(CONFIG_KVM)
 static void __fpstate_reset(struct fpstate *fpstate);
 
+static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
+{
+	struct fpu_state_perm *fpuperm;
+	u64 perm;
+
+	if (!IS_ENABLED(CONFIG_X86_64))
+		return;
+
+	spin_lock_irq(&current->sighand->siglock);
+	fpuperm = &current->group_leader->thread.fpu.guest_perm;
+	perm = fpuperm->__state_perm;
+
+	/* First fpstate allocation locks down permissions. */
+	WRITE_ONCE(fpuperm->__state_perm, perm | FPU_GUEST_PERM_LOCKED);
+
+	spin_unlock_irq(&current->sighand->siglock);
+
+	gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
+}
+
 bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 {
 	struct fpstate *fpstate;
@@ -216,7 +236,11 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	fpstate->is_valloc	= true;
 	fpstate->is_guest	= true;
 
-	gfpu->fpstate = fpstate;
+	gfpu->fpstate		= fpstate;
+	gfpu->xfeatures		= fpu_user_cfg.default_features;
+	gfpu->perm		= fpu_user_cfg.default_features;
+	fpu_init_guest_permissions(gfpu);
+
 	return true;
 }
 EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);

[PATCH v5 03/21] kvm: x86: Fix xstate_required_size() to follow XSTATE alignment rule

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

CPUID.0xD.1.EBX enumerates the size of the XSAVE area (in compacted
format) required by XSAVES. If CPUID.0xD.i.ECX[1] is set for a state
component (i), this state component should be located on the next
64-bytes boundary following the preceding state component in the
compacted layout.

Fix xstate_required_size() to follow the alignment rule. AMX is the
first state component with 64-bytes alignment to catch this bug.

Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/cpuid.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0b920e12bb6d..f3e6fda6b858 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -42,7 +42,11 @@ static u32 xstate_required_size(u64 xstate_bv, bool compacted)
 		if (xstate_bv & 0x1) {
 		        u32 eax, ebx, ecx, edx, offset;
 		        cpuid_count(0xD, feature_bit, &eax, &ebx, &ecx, &edx);
-			offset = compacted ? ret : ebx;
+			/* ECX[1]: 64B alignment in compacted form */
+			if (compacted)
+				offset = (ecx & 0x2) ? ALIGN(ret, 64) : ret;
+			else
+				offset = ebx;
 			ret = max(ret, offset + eax);
 		}
 

[PATCH v5 04/21] kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

KVM_GET_SUPPORTED_CPUID should not include any dynamic xstates in
CPUID[0xD] if they have not been requested with prctl. Otherwise
a process which directly passes KVM_GET_SUPPORTED_CPUID to
KVM_SET_CPUID2 would now fail even if it doesn't intend to use a
dynamically enabled feature. Userspace must know that prctl is
required and allocate >4K xstate buffer before setting any dynamic
bit.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 Documentation/virt/kvm/api.rst | 4 ++++
 arch/x86/kvm/cpuid.c           | 9 ++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 6b683dfea8f2..f4ea5e41a4d0 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1687,6 +1687,10 @@ userspace capabilities, and with user requirements (for example, the
 user may wish to constrain cpuid to emulate older hardware, or for
 feature consistency across a cluster).
 
+Dynamically-enabled feature bits need to be requested with
+``arch_prctl()`` before calling this ioctl. Feature bits that have not
+been requested are excluded from the result.
+
 Note that certain capabilities, such as KVM_CAP_X86_DISABLE_EXITS, may
 expose cpuid features (e.g. MONITOR) which are not supported by kvm in
 its default configuration. If userspace enables such capabilities, it
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f3e6fda6b858..eb52dde5deec 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -815,11 +815,13 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 				goto out;
 		}
 		break;
-	case 0xd:
-		entry->eax &= supported_xcr0;
+	case 0xd: {
+		u64 guest_perm = xstate_get_guest_group_perm();
+
+		entry->eax &= supported_xcr0 & guest_perm;
 		entry->ebx = xstate_required_size(supported_xcr0, false);
 		entry->ecx = entry->ebx;
-		entry->edx &= supported_xcr0 >> 32;
+		entry->edx &= (supported_xcr0 & guest_perm) >> 32;
 		if (!supported_xcr0)
 			break;
 
@@ -866,6 +868,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			entry->edx = 0;
 		}
 		break;
+	}
 	case 0x12:
 		/* Intel SGX */
 		if (!kvm_cpu_cap_has(X86_FEATURE_SGX)) {

[PATCH v5 05/21] x86/fpu: Make XFD initialization in __fpstate_reset() a function argument

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

vCPU threads are different from native tasks regarding to the initial XFD
value. While all native tasks follow a fixed value (init_fpstate::xfd)
established by the FPU core at boot, vCPU threads need to obey the reset
value (i.e. ZERO) defined by the specification, to meet the expectation of
the guest.

Let the caller supply an argument and adjust the host and guest related
invocations accordingly.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kernel/fpu/core.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index eddeeb4ed2f5..a78bc547fc03 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -199,7 +199,7 @@ void fpu_reset_from_exception_fixup(void)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate);
+static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
 
 static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 {
@@ -231,7 +231,8 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	if (!fpstate)
 		return false;
 
-	__fpstate_reset(fpstate);
+	/* Leave xfd to 0 (the reset value defined by spec) */
+	__fpstate_reset(fpstate, 0);
 	fpstate_init_user(fpstate);
 	fpstate->is_valloc	= true;
 	fpstate->is_guest	= true;
@@ -454,21 +455,21 @@ void fpstate_init_user(struct fpstate *fpstate)
 		fpstate_init_fstate(fpstate);
 }
 
-static void __fpstate_reset(struct fpstate *fpstate)
+static void __fpstate_reset(struct fpstate *fpstate, u64 xfd)
 {
 	/* Initialize sizes and feature masks */
 	fpstate->size		= fpu_kernel_cfg.default_size;
 	fpstate->user_size	= fpu_user_cfg.default_size;
 	fpstate->xfeatures	= fpu_kernel_cfg.default_features;
 	fpstate->user_xfeatures	= fpu_user_cfg.default_features;
-	fpstate->xfd		= init_fpstate.xfd;
+	fpstate->xfd		= xfd;
 }
 
 void fpstate_reset(struct fpu *fpu)
 {
 	/* Set the fpstate pointer to the default fpstate */
 	fpu->fpstate = &fpu->__fpstate;
-	__fpstate_reset(fpu->fpstate);
+	__fpstate_reset(fpu->fpstate, init_fpstate.xfd);
 
 	/* Initialize the permission related info in fpu */
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;

[PATCH v5 06/21] x86/fpu: Add guest support to xfd_enable_feature()

[Yang Zhong]

From: Thomas Gleixner <tglx@linutronix.de>

Guest support for dynamically enabled FPU features requires a few
modifications to the enablement function which is currently invoked from
the #NM handler:

  1) Use guest permissions and sizes for the update

  2) Update fpu_guest state accordingly

  3) Take into account that the enabling can be triggered either from a
     running guest via XSETBV and MSR_IA32_XFD write emulation or from
     a guest restore. In the latter case the guests fpstate is not the
     current tasks active fpstate.

Split the function and implement the guest mechanics throughout the
callchain.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kernel/fpu/xstate.c | 93 +++++++++++++++++++++---------------
 arch/x86/kernel/fpu/xstate.h |  2 +
 2 files changed, 56 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 5f01d463859d..0c0b2323cdec 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1499,29 +1499,6 @@ void fpstate_free(struct fpu *fpu)
 		vfree(fpu->fpstate);
 }
 
-/**
- * fpu_install_fpstate - Update the active fpstate in the FPU
- *
- * @fpu:	A struct fpu * pointer
- * @newfps:	A struct fpstate * pointer
- *
- * Returns:	A null pointer if the last active fpstate is the embedded
- *		one or the new fpstate is already installed;
- *		otherwise, a pointer to the old fpstate which has to
- *		be freed by the caller.
- */
-static struct fpstate *fpu_install_fpstate(struct fpu *fpu,
-					   struct fpstate *newfps)
-{
-	struct fpstate *oldfps = fpu->fpstate;
-
-	if (fpu->fpstate == newfps)
-		return NULL;
-
-	fpu->fpstate = newfps;
-	return oldfps != &fpu->__fpstate ? oldfps : NULL;
-}
-
 /**
  * fpstate_realloc - Reallocate struct fpstate for the requested new features
  *
@@ -1529,6 +1506,7 @@ static struct fpstate *fpu_install_fpstate(struct fpu *fpu,
  *		of that task
  * @ksize:	The required size for the kernel buffer
  * @usize:	The required size for user space buffers
+ * @guest_fpu:	Pointer to a guest FPU container. NULL for host allocations
  *
  * Note vs. vmalloc(): If the task with a vzalloc()-allocated buffer
  * terminates quickly, vfree()-induced IPIs may be a concern, but tasks
@@ -1537,13 +1515,13 @@ static struct fpstate *fpu_install_fpstate(struct fpu *fpu,
  * Returns: 0 on success, -ENOMEM on allocation error.
  */
 static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
-			   unsigned int usize)
+			   unsigned int usize, struct fpu_guest *guest_fpu)
 {
 	struct fpu *fpu = &current->thread.fpu;
 	struct fpstate *curfps, *newfps = NULL;
 	unsigned int fpsize;
+	bool in_use;
 
-	curfps = fpu->fpstate;
 	fpsize = ksize + ALIGN(offsetof(struct fpstate, regs), 64);
 
 	newfps = vzalloc(fpsize);
@@ -1553,28 +1531,55 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
 	newfps->user_size = usize;
 	newfps->is_valloc = true;
 
+	/*
+	 * When a guest FPU is supplied, use @guest_fpu->fpstate
+	 * as reference independent whether it is in use or not.
+	 */
+	curfps = guest_fpu ? guest_fpu->fpstate : fpu->fpstate;
+
+	/* Determine whether @curfps is the active fpstate */
+	in_use = fpu->fpstate == curfps;
+
+	if (guest_fpu) {
+		newfps->is_guest = true;
+		newfps->is_confidential = curfps->is_confidential;
+		newfps->in_use = curfps->in_use;
+		guest_fpu->xfeatures |= xfeatures;
+	}
+
 	fpregs_lock();
 	/*
-	 * Ensure that the current state is in the registers before
-	 * swapping fpstate as that might invalidate it due to layout
-	 * changes.
+	 * If @curfps is in use, ensure that the current state is in the
+	 * registers before swapping fpstate as that might invalidate it
+	 * due to layout changes.
 	 */
-	if (test_thread_flag(TIF_NEED_FPU_LOAD))
+	if (in_use && test_thread_flag(TIF_NEED_FPU_LOAD))
 		fpregs_restore_userregs();
 
 	newfps->xfeatures = curfps->xfeatures | xfeatures;
 	newfps->user_xfeatures = curfps->user_xfeatures | xfeatures;
 	newfps->xfd = curfps->xfd & ~xfeatures;
 
-	curfps = fpu_install_fpstate(fpu, newfps);
-
 	/* Do the final updates within the locked region */
 	xstate_init_xcomp_bv(&newfps->regs.xsave, newfps->xfeatures);
-	xfd_update_state(newfps);
 
+	if (guest_fpu) {
+		guest_fpu->fpstate = newfps;
+		/* If curfps is active, update the FPU fpstate pointer */
+		if (in_use)
+			fpu->fpstate = newfps;
+	} else {
+		fpu->fpstate = newfps;
+	}
+
+	if (in_use)
+		xfd_update_state(fpu->fpstate);
 	fpregs_unlock();
 
-	vfree(curfps);
+	/* Only free valloc'ed state */
+	if (curfps && curfps->is_valloc)
+		vfree(curfps);
+
 	return 0;
 }
 
@@ -1682,14 +1687,16 @@ static int xstate_request_perm(unsigned long idx, bool guest)
 	return ret;
 }
 
-int xfd_enable_feature(u64 xfd_err)
+int __xfd_enable_feature(u64 xfd_err, struct fpu_guest *guest_fpu)
 {
 	u64 xfd_event = xfd_err & XFEATURE_MASK_USER_DYNAMIC;
+	struct fpu_state_perm *perm;
 	unsigned int ksize, usize;
 	struct fpu *fpu;
 
 	if (!xfd_event) {
-		pr_err_once("XFD: Invalid xfd error: %016llx\n", xfd_err);
+		if (!guest_fpu)
+			pr_err_once("XFD: Invalid xfd error: %016llx\n", xfd_err);
 		return 0;
 	}
 
@@ -1697,14 +1704,16 @@ int xfd_enable_feature(u64 xfd_err)
 	spin_lock_irq(&current->sighand->siglock);
 
 	/* If not permitted let it die */
-	if ((xstate_get_host_group_perm() & xfd_event) != xfd_event) {
+	if ((xstate_get_group_perm(!!guest_fpu) & xfd_event) != xfd_event) {
 		spin_unlock_irq(&current->sighand->siglock);
 		return -EPERM;
 	}
 
 	fpu = &current->group_leader->thread.fpu;
-	ksize = fpu->perm.__state_size;
-	usize = fpu->perm.__user_state_size;
+	perm = guest_fpu ? &fpu->guest_perm : &fpu->perm;
+	ksize = perm->__state_size;
+	usize = perm->__user_state_size;
+
 	/*
 	 * The feature is permitted. State size is sufficient.  Dropping
 	 * the lock is safe here even if more features are added from
@@ -1717,10 +1726,16 @@ int xfd_enable_feature(u64 xfd_err)
 	 * Try to allocate a new fpstate. If that fails there is no way
 	 * out.
 	 */
-	if (fpstate_realloc(xfd_event, ksize, usize))
+	if (fpstate_realloc(xfd_event, ksize, usize, guest_fpu))
 		return -EFAULT;
 	return 0;
 }
+
+int xfd_enable_feature(u64 xfd_err)
+{
+	return __xfd_enable_feature(xfd_err, NULL);
+}
+
 #else /* CONFIG_X86_64 */
 static inline int xstate_request_perm(unsigned long idx, bool guest)
 {
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 98a472775c97..3e63f723525b 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -55,6 +55,8 @@ extern void fpu__init_system_xstate(unsigned int legacy_size);
 
 extern void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
 
+extern int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu);
+
 static inline u64 xfeatures_mask_supervisor(void)
 {
 	return fpu_kernel_cfg.max_features & XFEATURE_MASK_SUPERVISOR_SUPPORTED;

[PATCH v5 07/21] x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM

[Yang Zhong]

From: Sean Christopherson <seanjc@google.com>

Provide a wrapper for expanding the guest fpstate buffer according
to requested xfeatures. KVM wants to call this wrapper to manage
any dynamic xstate used by the guest.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/api.h |  1 +
 arch/x86/kernel/fpu/core.c     | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index d8c222290e68..1ed2a247a84e 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -138,6 +138,7 @@ extern inline u64 xstate_get_guest_group_perm(void);
 extern bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu);
 extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
 extern int fpu_swap_kvm_fpstate(struct fpu_guest *gfpu, bool enter_guest);
+extern int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures);
 
 extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
 extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index a78bc547fc03..5b08d20a4005 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -261,6 +261,23 @@ void fpu_free_guest_fpstate(struct fpu_guest *gfpu)
 }
 EXPORT_SYMBOL_GPL(fpu_free_guest_fpstate);
 
+int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures)
+{
+	lockdep_assert_preemption_enabled();
+
+	/* Nothing to do if all requested features are already enabled. */
+	xfeatures &= ~guest_fpu->xfeatures;
+	if (!xfeatures)
+		return 0;
+
+	/* Dynamic xfeatures are not supported with 32-bit kernels. */
+	if (!IS_ENABLED(CONFIG_X86_64))
+		return 0;
+
+	return __xfd_enable_feature(xfeatures, guest_fpu);
+}
+EXPORT_SYMBOL_GPL(fpu_enable_guest_xfd_features);
+
 int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
 {
 	struct fpstate *guest_fps = guest_fpu->fpstate;

[PATCH v5 08/21] kvm: x86: Enable dynamic xfeatures at KVM_SET_CPUID2

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

KVM can request fpstate expansion in two approaches:

  1) When intercepting guest updates to XCR0 and XFD MSR;

  2) Before vcpu runs (e.g. at KVM_SET_CPUID2);

The first option doesn't waste memory for legacy guest if it doesn't
support XFD. However doing so introduces more complexity and also
imposes an order requirement in the restoring path, i.e. XCR0/XFD
must be restored before XSTATE.

Given that the agreement is to do the static approach. This is
considered a better tradeoff though it does waste 8K memory for
legacy guest if its CPUID includes dynamically-enabled xfeatures.

Successful fpstate expansion requires userspace VMM to acquire
guest xstate permissions before calling KVM_SET_CPUID2.

Also take the chance to adjust the indent in kvm_set_cpuid().

Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/cpuid.c | 42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index eb52dde5deec..a0fedf1514ab 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -84,9 +84,12 @@ static inline struct kvm_cpuid_entry2 *cpuid_entry2_find(
 	return NULL;
 }
 
-static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
+static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
+			   struct kvm_cpuid_entry2 *entries,
+			   int nent)
 {
 	struct kvm_cpuid_entry2 *best;
+	u64 xfeatures;
 
 	/*
 	 * The existing code assumes virtual address is 48-bit or 57-bit in the
@@ -100,7 +103,20 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
 			return -EINVAL;
 	}
 
-	return 0;
+	/*
+	 * Exposing dynamic xfeatures to the guest requires additional
+	 * enabling in the FPU, e.g. to expand the guest XSAVE state size.
+	 */
+	best = cpuid_entry2_find(entries, nent, 0xd, 0);
+	if (!best)
+		return 0;
+
+	xfeatures = best->eax | ((u64)best->edx << 32);
+	xfeatures &= XFEATURE_MASK_USER_DYNAMIC;
+	if (!xfeatures)
+		return 0;
+
+	return fpu_enable_guest_xfd_features(&vcpu->arch.guest_fpu, xfeatures);
 }
 
 static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
@@ -280,21 +296,21 @@ u64 kvm_vcpu_reserved_gpa_bits_raw(struct kvm_vcpu *vcpu)
 static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
                         int nent)
 {
-    int r;
+	int r;
 
-    r = kvm_check_cpuid(e2, nent);
-    if (r)
-        return r;
+	r = kvm_check_cpuid(vcpu, e2, nent);
+	if (r)
+		return r;
 
-    kvfree(vcpu->arch.cpuid_entries);
-    vcpu->arch.cpuid_entries = e2;
-    vcpu->arch.cpuid_nent = nent;
+	kvfree(vcpu->arch.cpuid_entries);
+	vcpu->arch.cpuid_entries = e2;
+	vcpu->arch.cpuid_nent = nent;
 
-    kvm_update_kvm_cpuid_base(vcpu);
-    kvm_update_cpuid_runtime(vcpu);
-    kvm_vcpu_after_set_cpuid(vcpu);
+	kvm_update_kvm_cpuid_base(vcpu);
+	kvm_update_cpuid_runtime(vcpu);
+	kvm_vcpu_after_set_cpuid(vcpu);
 
-    return 0;
+	return 0;
 }
 
 /* when an old userspace process fills a new kernel module */

[PATCH v5 09/21] x86/fpu: Provide fpu_update_guest_xfd() for IA32_XFD emulation

[Yang Zhong]

From: Kevin Tian <kevin.tian@intel.com>

Guest XFD can be updated either in the emulation path or in the
restore path.

Provide a wrapper to update guest_fpu::fpstate::xfd. If the guest
fpstate is currently in-use, also update the per-cpu xfd cache and
the actual MSR.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/api.h |  6 ++++++
 arch/x86/kernel/fpu/core.c     | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 1ed2a247a84e..e4d10155290b 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -140,6 +140,12 @@ extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
 extern int fpu_swap_kvm_fpstate(struct fpu_guest *gfpu, bool enter_guest);
 extern int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures);
 
+#ifdef CONFIG_X86_64
+extern void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd);
+#else
+static inline void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd) { }
+#endif
+
 extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
 extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
 
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 5b08d20a4005..8f7f9bfc2506 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -278,6 +278,18 @@ int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures)
 }
 EXPORT_SYMBOL_GPL(fpu_enable_guest_xfd_features);
 
+#ifdef CONFIG_X86_64
+void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd)
+{
+	fpregs_lock();
+	guest_fpu->fpstate->xfd = xfd;
+	if (guest_fpu->fpstate->in_use)
+		xfd_update_state(guest_fpu->fpstate);
+	fpregs_unlock();
+}
+EXPORT_SYMBOL_GPL(fpu_update_guest_xfd);
+#endif /* CONFIG_X86_64 */
+
 int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
 {
 	struct fpstate *guest_fps = guest_fpu->fpstate;

[PATCH v5 10/21] kvm: x86: Add emulation for IA32_XFD

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

Intel's eXtended Feature Disable (XFD) feature allows the software
to dynamically adjust fpstate buffer size for XSAVE features which
have large state.

Because guest fpstate has been expanded for all possible dynamic
xstates at KVM_SET_CPUID2, emulation of the IA32_XFD MSR is
straightforward. For write just call fpu_update_guest_xfd() to
update the guest fpu container once all the sanity checks are passed.
For read simply return the cached value in the container.

Signed-off-by: Zeng Guang <guang.zeng@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/x86.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c194a8cbd25f..21ce65220e38 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1377,6 +1377,7 @@ static const u32 msrs_to_save_all[] = {
 	MSR_F15H_PERF_CTL3, MSR_F15H_PERF_CTL4, MSR_F15H_PERF_CTL5,
 	MSR_F15H_PERF_CTR0, MSR_F15H_PERF_CTR1, MSR_F15H_PERF_CTR2,
 	MSR_F15H_PERF_CTR3, MSR_F15H_PERF_CTR4, MSR_F15H_PERF_CTR5,
+	MSR_IA32_XFD,
 };
 
 static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
@@ -3686,6 +3687,19 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 1;
 		vcpu->arch.msr_misc_features_enables = data;
 		break;
+#ifdef CONFIG_X86_64
+	case MSR_IA32_XFD:
+		if (!msr_info->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
+			return 1;
+
+		if (data & ~(XFEATURE_MASK_USER_DYNAMIC &
+			     vcpu->arch.guest_supported_xcr0))
+			return 1;
+
+		fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
+		break;
+#endif
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr))
 			return kvm_pmu_set_msr(vcpu, msr_info);
@@ -4006,6 +4020,15 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_K7_HWCR:
 		msr_info->data = vcpu->arch.msr_hwcr;
 		break;
+#ifdef CONFIG_X86_64
+	case MSR_IA32_XFD:
+		if (!msr_info->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
+			return 1;
+
+		msr_info->data = vcpu->arch.guest_fpu.fpstate->xfd;
+		break;
+#endif
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
 			return kvm_pmu_get_msr(vcpu, msr_info);
@@ -6441,6 +6464,10 @@ static void kvm_init_msr_list(void)
 			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
 				continue;
 			break;
+		case MSR_IA32_XFD:
+			if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
+				continue;
+			break;
 		default:
 			break;
 		}

[PATCH v5 11/21] x86/fpu: Prepare xfd_err in struct fpu_guest

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

When XFD causes an instruction to generate #NM, IA32_XFD_ERR
contains information about which disabled state components are
being accessed. The #NM handler is expected to check this
information and then enable the state components by clearing
IA32_XFD for the faulting task (if having permission).

If the XFD_ERR value generated in guest is consumed/clobbered
by the host before the guest itself doing so, it may lead to
non-XFD-related #NM treated as XFD #NM in host (due to non-zero
value in XFD_ERR), or XFD-related #NM treated as non-XFD #NM in
guest (XFD_ERR cleared by the host #NM handler).

Introduce a new field in fpu_guest to save the guest xfd_err value.
KVM is expected to save guest xfd_err before interrupt is enabled
and restore it right before entering the guest (with interrupt
disabled).

Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/types.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index c752d0aa23a4..3795d0573773 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -517,6 +517,11 @@ struct fpu_guest {
 	 */
 	u64				perm;
 
+	/*
+	 * @xfd_err:			Save the guest value.
+	 */
+	u64				xfd_err;
+
 	/*
 	 * @fpstate:			Pointer to the allocated guest fpstate
 	 */

[PATCH v5 12/21] kvm: x86: Intercept #NM for saving IA32_XFD_ERR

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

Guest IA32_XFD_ERR is generally modified in two places:

  - Set by CPU when #NM is triggered;
  - Cleared by guest in its #NM handler;

Intercept #NM for the first case when a nonzero value is written
to IA32_XFD. Nonzero indicates that the guest is willing to do
dynamic fpstate expansion for certain xfeatures, thus KVM needs to
manage and virtualize guest XFD_ERR properly. The vcpu exception
bitmap is updated in XFD write emulation according to guest_fpu::xfd.

Save the current XFD_ERR value to the guest_fpu container in the #NM
VM-exit handler. This must be done with interrupt disabled, otherwise
the unsaved MSR value may be clobbered by host activity.

The saving operation is conducted conditionally only when guest_fpu:xfd
includes a non-zero value. Doing so also avoids misread on a platform
which doesn't support XFD but #NM is triggered due to L1 interception.

Queueing #NM to the guest is postponed to handle_exception_nmi(). This
goes through the nested_vmx check so a virtual vmexit is queued instead
when #NM is triggered in L2 but L1 wants to intercept it.

Restore the host value (always ZERO outside of the host #NM
handler) before enabling interrupt.

Restore the guest value from the guest_fpu container right before
entering the guest (with interrupt disabled).

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/vmx/vmcs.h |  5 +++++
 arch/x86/kvm/vmx/vmx.c  | 48 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c      |  6 ++++++
 3 files changed, 59 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h
index 6e5de2e2b0da..e325c290a816 100644
--- a/arch/x86/kvm/vmx/vmcs.h
+++ b/arch/x86/kvm/vmx/vmcs.h
@@ -129,6 +129,11 @@ static inline bool is_machine_check(u32 intr_info)
 	return is_exception_n(intr_info, MC_VECTOR);
 }
 
+static inline bool is_nm_fault(u32 intr_info)
+{
+	return is_exception_n(intr_info, NM_VECTOR);
+}
+
 /* Undocumented: icebp/int1 */
 static inline bool is_icebp(u32 intr_info)
 {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fe06b02994e6..939e6aad128c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -36,6 +36,7 @@
 #include <asm/debugreg.h>
 #include <asm/desc.h>
 #include <asm/fpu/api.h>
+#include <asm/fpu/xstate.h>
 #include <asm/idtentry.h>
 #include <asm/io.h>
 #include <asm/irq_remapping.h>
@@ -761,6 +762,13 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu)
 		vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, match);
 	}
 
+	/*
+	 * Trap #NM if guest xfd contains a non-zero value so guest XFD_ERR
+	 * can be saved timely.
+	 */
+	if (vcpu->arch.guest_fpu.fpstate->xfd)
+		eb |= (1u << NM_VECTOR);
+
 	vmcs_write32(EXCEPTION_BITMAP, eb);
 }
 
@@ -1967,6 +1975,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_KERNEL_GS_BASE:
 		vmx_write_guest_kernel_gs_base(vmx, data);
 		break;
+	case MSR_IA32_XFD:
+		ret = kvm_set_msr_common(vcpu, msr_info);
+		/* Update #NM interception according to guest xfd */
+		if (!ret)
+			vmx_update_exception_bitmap(vcpu);
+		break;
 #endif
 	case MSR_IA32_SYSENTER_CS:
 		if (is_guest_mode(vcpu))
@@ -4798,6 +4812,17 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 	if (is_machine_check(intr_info) || is_nmi(intr_info))
 		return 1; /* handled by handle_exception_nmi_irqoff() */
 
+	/*
+	 * Queue the exception here instead of in handle_nm_fault_irqoff().
+	 * This ensures the nested_vmx check is not skipped so vmexit can
+	 * be reflected to L1 (when it intercepts #NM) before reaching this
+	 * point.
+	 */
+	if (is_nm_fault(intr_info)) {
+		kvm_queue_exception(vcpu, NM_VECTOR);
+		return 1;
+	}
+
 	if (is_invalid_opcode(intr_info))
 		return handle_ud(vcpu);
 
@@ -6399,6 +6424,26 @@ static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu,
 	kvm_after_interrupt(vcpu);
 }
 
+static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * Save xfd_err to guest_fpu before interrupt is enabled, so the
+	 * MSR value is not clobbered by the host activity before the guest
+	 * has chance to consume it.
+	 *
+	 * We should not blindly read xfd_err here, since this exception
+	 * might be caused by L1 interception on a platform which doesn't
+	 * support xfd at all.
+	 *
+	 * Do it conditionally upon guest_fpu::xfd. xfd_err matters
+	 * only when xfd contains a non-zero value.
+	 *
+	 * Queuing exception is done in vmx_handle_exit. See comment there.
+	 */
+	if (vcpu->arch.guest_fpu.fpstate->xfd)
+		rdmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
+}
+
 static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
 {
 	const unsigned long nmi_entry = (unsigned long)asm_exc_nmi_noist;
@@ -6407,6 +6452,9 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
 	/* if exit due to PF check for async PF */
 	if (is_page_fault(intr_info))
 		vmx->vcpu.arch.apf.host_apf_flags = kvm_read_and_reset_apf_flags();
+	/* if exit due to NM, handle before interrupts are enabled */
+	else if (is_nm_fault(intr_info))
+		handle_nm_fault_irqoff(&vmx->vcpu);
 	/* Handle machine checks before interrupts are enabled */
 	else if (is_machine_check(intr_info))
 		kvm_machine_check();
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 21ce65220e38..2c988f8ca616 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9953,6 +9953,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 
+	if (vcpu->arch.guest_fpu.xfd_err)
+		wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
+
 	if (unlikely(vcpu->arch.switch_db_regs)) {
 		set_debugreg(0, 7);
 		set_debugreg(vcpu->arch.eff_db[0], 0);
@@ -10016,6 +10019,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	static_call(kvm_x86_handle_exit_irqoff)(vcpu);
 
+	if (vcpu->arch.guest_fpu.xfd_err)
+		wrmsrl(MSR_IA32_XFD_ERR, 0);
+
 	/*
 	 * Consume any pending interrupts, including the possible source of
 	 * VM-Exit on SVM and any ticks that occur between VM-Exit and now.

[PATCH v5 13/21] kvm: x86: Emulate IA32_XFD_ERR for guest

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

Emulate read/write to IA32_XFD_ERR MSR.

Only the saved value in the guest_fpu container is touched in the
emulation handler. Actual MSR update is handled right before entering
the guest (with preemption disabled)

Signed-off-by: Zeng Guang <guang.zeng@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/x86.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2c988f8ca616..434986928552 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1377,7 +1377,7 @@ static const u32 msrs_to_save_all[] = {
 	MSR_F15H_PERF_CTL3, MSR_F15H_PERF_CTL4, MSR_F15H_PERF_CTL5,
 	MSR_F15H_PERF_CTR0, MSR_F15H_PERF_CTR1, MSR_F15H_PERF_CTR2,
 	MSR_F15H_PERF_CTR3, MSR_F15H_PERF_CTR4, MSR_F15H_PERF_CTR5,
-	MSR_IA32_XFD,
+	MSR_IA32_XFD, MSR_IA32_XFD_ERR,
 };
 
 static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
@@ -3699,6 +3699,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 		fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
 		break;
+	case MSR_IA32_XFD_ERR:
+		if (!msr_info->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
+			return 1;
+
+		if (data & ~(XFEATURE_MASK_USER_DYNAMIC &
+			     vcpu->arch.guest_supported_xcr0))
+			return 1;
+
+		vcpu->arch.guest_fpu.xfd_err = data;
+		break;
 #endif
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr))
@@ -4028,6 +4039,13 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 		msr_info->data = vcpu->arch.guest_fpu.fpstate->xfd;
 		break;
+	case MSR_IA32_XFD_ERR:
+		if (!msr_info->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
+			return 1;
+
+		msr_info->data = vcpu->arch.guest_fpu.xfd_err;
+		break;
 #endif
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
@@ -6465,6 +6483,7 @@ static void kvm_init_msr_list(void)
 				continue;
 			break;
 		case MSR_IA32_XFD:
+		case MSR_IA32_XFD_ERR:
 			if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
 				continue;
 			break;

[PATCH v5 14/21] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

This saves one unnecessary VM-exit in guest #NM handler, given that the
MSR is already restored with the guest value before the guest is resumed.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 6 ++++++
 arch/x86/kvm/vmx/vmx.h | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 939e6aad128c..b601dc8a7f13 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
 	MSR_FS_BASE,
 	MSR_GS_BASE,
 	MSR_KERNEL_GS_BASE,
+	MSR_IA32_XFD_ERR,
 #endif
 	MSR_IA32_SYSENTER_CS,
 	MSR_IA32_SYSENTER_ESP,
@@ -7290,6 +7291,11 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		}
 	}
 
+	if (kvm_cpu_cap_has(X86_FEATURE_XFD))
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R,
+					  !guest_cpuid_has(vcpu, X86_FEATURE_XFD));
+
+
 	set_cr4_guest_host_mask(vmx);
 
 	vmx_write_encls_bitmap(vcpu, NULL);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index acb874db02da..e0922c80c9d1 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -352,7 +352,7 @@ struct vcpu_vmx {
 	struct lbr_desc lbr_desc;
 
 	/* Save desired MSR intercept (read: pass-through) state */
-#define MAX_POSSIBLE_PASSTHROUGH_MSRS	13
+#define MAX_POSSIBLE_PASSTHROUGH_MSRS	14
 	struct {
 		DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
 		DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);

[PATCH v5 15/21] kvm: x86: Add XCR0 support for Intel AMX

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

Two XCR0 bits are defined for AMX to support XSAVE mechanism. Bit 17
is for tilecfg and bit 18 is for tiledata.

The value of XCR0[17:18] is always either 00b or 11b. Also, SDM
recommends that only 64-bit operating systems enable Intel AMX by
setting XCR0[18:17]. 32-bit host kernel never sets the tile bits in
vcpu->arch.guest_supported_xcr0.

Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/kvm/x86.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 434986928552..553e4af12edc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -211,7 +211,7 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
 #define KVM_SUPPORTED_XCR0     (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
 				| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
 				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
-				| XFEATURE_MASK_PKRU)
+				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
 
 u64 __read_mostly host_efer;
 EXPORT_SYMBOL_GPL(host_efer);
@@ -1010,6 +1010,11 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 		if ((xcr0 & XFEATURE_MASK_AVX512) != XFEATURE_MASK_AVX512)
 			return 1;
 	}
+
+	if ((xcr0 & XFEATURE_MASK_XTILE) &&
+	    ((xcr0 & XFEATURE_MASK_XTILE) != XFEATURE_MASK_XTILE))
+		return 1;
+
 	vcpu->arch.xcr0 = xcr0;
 
 	if ((xcr0 ^ old_xcr0) & XFEATURE_MASK_EXTEND)

[PATCH v5 16/21] kvm: x86: Add CPUID support for Intel AMX

[Yang Zhong]

From: Jing Liu <jing2.liu@intel.com>

Extend CPUID emulation to support XFD, AMX_TILE, AMX_INT8 and
AMX_BF16. Adding those bits into kvm_cpu_caps finally activates all
previous logics in this series.

Hide XFD on 32bit host kernels. Otherwise it leads to a weird situation
where KVM tells userspace to migrate MSR_IA32_XFD and then rejects
attempts to read/write the MSR.

Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/cpufeatures.h |  2 ++
 arch/x86/kvm/cpuid.c               | 27 +++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index d5b5f2ab87a0..da872b6f8d8b 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -299,7 +299,9 @@
 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
 #define X86_FEATURE_AVX512_BF16		(12*32+ 5) /* AVX512 BFLOAT16 instructions */
+#define X86_FEATURE_AMX_BF16		(18*32+22) /* AMX bf16 Support */
 #define X86_FEATURE_AMX_TILE		(18*32+24) /* AMX tile Support */
+#define X86_FEATURE_AMX_INT8		(18*32+25) /* AMX int8 Support */
 
 /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */
 #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index a0fedf1514ab..ba4c3d5d2386 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -442,9 +442,11 @@ void kvm_set_cpu_caps(void)
 #ifdef CONFIG_X86_64
 	unsigned int f_gbpages = F(GBPAGES);
 	unsigned int f_lm = F(LM);
+	unsigned int f_xfd = F(XFD);
 #else
 	unsigned int f_gbpages = 0;
 	unsigned int f_lm = 0;
+	unsigned int f_xfd = 0;
 #endif
 	memset(kvm_cpu_caps, 0, sizeof(kvm_cpu_caps));
 
@@ -512,7 +514,8 @@ void kvm_set_cpu_caps(void)
 		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
 		F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) |
 		F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM) |
-		F(SERIALIZE) | F(TSXLDTRK) | F(AVX512_FP16)
+		F(SERIALIZE) | F(TSXLDTRK) | F(AVX512_FP16) |
+		F(AMX_TILE) | F(AMX_INT8) | F(AMX_BF16)
 	);
 
 	/* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software. */
@@ -531,7 +534,7 @@ void kvm_set_cpu_caps(void)
 	);
 
 	kvm_cpu_cap_mask(CPUID_D_1_EAX,
-		F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES)
+		F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES) | f_xfd
 	);
 
 	kvm_cpu_cap_init_scattered(CPUID_12_EAX,
@@ -657,6 +660,8 @@ static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array,
 	case 0x14:
 	case 0x17:
 	case 0x18:
+	case 0x1d:
+	case 0x1e:
 	case 0x1f:
 	case 0x8000001d:
 		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
@@ -929,6 +934,24 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 				goto out;
 		}
 		break;
+	/* Intel AMX TILE */
+	case 0x1d:
+		if (!kvm_cpu_cap_has(X86_FEATURE_AMX_TILE)) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+			break;
+		}
+
+		for (i = 1, max_idx = entry->eax; i <= max_idx; ++i) {
+			if (!do_host_cpuid(array, function, i))
+				goto out;
+		}
+		break;
+	case 0x1e: /* TMUL information */
+		if (!kvm_cpu_cap_has(X86_FEATURE_AMX_TILE)) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+			break;
+		}
+		break;
 	case KVM_CPUID_SIGNATURE: {
 		const u32 *sigptr = (const u32 *)KVM_SIGNATURE;
 		entry->eax = KVM_CPUID_FEATURES;

[PATCH v5 17/21] x86/fpu: Add uabi_size to guest_fpu

[Yang Zhong]

From: Thomas Gleixner <tglx@linutronix.de>

Userspace needs to inquire KVM about the buffer size to work
with the new KVM_SET_XSAVE and KVM_GET_XSAVE2. Add the size info
to guest_fpu for KVM to access.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/types.h | 5 +++++
 arch/x86/kernel/fpu/core.c       | 1 +
 arch/x86/kernel/fpu/xstate.c     | 1 +
 3 files changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 3795d0573773..eb7cd1139d97 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -522,6 +522,11 @@ struct fpu_guest {
 	 */
 	u64				xfd_err;
 
+	/*
+	 * @uabi_size:			Size required for save/restore
+	 */
+	unsigned int			uabi_size;
+
 	/*
 	 * @fpstate:			Pointer to the allocated guest fpstate
 	 */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 8f7f9bfc2506..5e7de79c1fe1 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -240,6 +240,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	gfpu->fpstate		= fpstate;
 	gfpu->xfeatures		= fpu_user_cfg.default_features;
 	gfpu->perm		= fpu_user_cfg.default_features;
+	gfpu->uabi_size		= fpu_user_cfg.default_size;
 	fpu_init_guest_permissions(gfpu);
 
 	return true;
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 0c0b2323cdec..10fe072f1c92 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1545,6 +1545,7 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
 		newfps->is_confidential = curfps->is_confidential;
 		newfps->in_use = curfps->in_use;
 		guest_fpu->xfeatures |= xfeatures;
+		guest_fpu->uabi_size = usize;
 	}
 
 	fpregs_lock();

[PATCH v5 18/21] kvm: x86: Add support for getting/setting expanded xstate buffer

[Yang Zhong]

From: Guang Zeng <guang.zeng@intel.com>

With KVM_CAP_XSAVE, userspace uses a hardcoded 4KB buffer to get/set
xstate data from/to KVM. This doesn't work when dynamic xfeatures
(e.g. AMX) are exposed to the guest as they require a larger buffer
size.

Introduce a new capability (KVM_CAP_XSAVE2). Userspace VMM gets the
required xstate buffer size via KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).
KVM_SET_XSAVE is extended to work with both legacy and new capabilities
by doing properly-sized memdup_user() based on the guest fpu container.
KVM_GET_XSAVE is kept for backward-compatible reason. Instead,
KVM_GET_XSAVE2 is introduced under KVM_CAP_XSAVE2 as the preferred
interface for getting xstate buffer (4KB or larger size) from KVM
(Link: https://lkml.org/lkml/2021/12/15/510)

Also, update the api doc with the new KVM_GET_XSAVE2 ioctl.

Signed-off-by: Guang Zeng <guang.zeng@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 Documentation/virt/kvm/api.rst  | 42 ++++++++++++++++++++++++++++--
 arch/x86/include/uapi/asm/kvm.h | 16 +++++++++++-
 arch/x86/kvm/cpuid.c            |  2 +-
 arch/x86/kvm/cpuid.h            |  2 ++
 arch/x86/kvm/x86.c              | 45 ++++++++++++++++++++++++++++++++-
 include/uapi/linux/kvm.h        |  4 +++
 6 files changed, 106 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index f4ea5e41a4d0..d3791a14eb9a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1569,6 +1569,7 @@ otherwise it will return EBUSY error.
 
   struct kvm_xsave {
 	__u32 region[1024];
+	__u32 extra[0];
   };
 
 This ioctl would copy current vcpu's xsave struct to the userspace.
@@ -1577,7 +1578,7 @@ This ioctl would copy current vcpu's xsave struct to the userspace.
 4.43 KVM_SET_XSAVE
 ------------------
 
-:Capability: KVM_CAP_XSAVE
+:Capability: KVM_CAP_XSAVE and KVM_CAP_XSAVE2
 :Architectures: x86
 :Type: vcpu ioctl
 :Parameters: struct kvm_xsave (in)
@@ -1588,9 +1589,18 @@ This ioctl would copy current vcpu's xsave struct to the userspace.
 
   struct kvm_xsave {
 	__u32 region[1024];
+	__u32 extra[0];
   };
 
-This ioctl would copy userspace's xsave struct to the kernel.
+This ioctl would copy userspace's xsave struct to the kernel. It copies
+as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2),
+when invoked on the vm file descriptor. The size value returned by
+KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096.
+Currently, it is only greater than 4096 if a dynamic feature has been
+enabled with ``arch_prctl()``, but this may change in the future.
+
+The offsets of the state save areas in struct kvm_xsave follow the
+contents of CPUID leaf 0xD on the host.
 
 
 4.44 KVM_GET_XCRS
@@ -5535,6 +5545,34 @@ the trailing ``'\0'``, is indicated by ``name_size`` in the header.
 The Stats Data block contains an array of 64-bit values in the same order
 as the descriptors in Descriptors block.
 
+4.42 KVM_GET_XSAVE2
+------------------
+
+:Capability: KVM_CAP_XSAVE2
+:Architectures: x86
+:Type: vcpu ioctl
+:Parameters: struct kvm_xsave (out)
+:Returns: 0 on success, -1 on error
+
+
+::
+
+  struct kvm_xsave {
+	__u32 region[1024];
+	__u32 extra[0];
+  };
+
+This ioctl would copy current vcpu's xsave struct to the userspace. It
+copies as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+when invoked on the vm file descriptor. The size value returned by
+KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096.
+Currently, it is only greater than 4096 if a dynamic feature has been
+enabled with ``arch_prctl()``, but this may change in the future.
+
+The offsets of the state save areas in struct kvm_xsave follow the contents
+of CPUID leaf 0xD on the host.
+
+
 5. The kvm_run structure
 ========================
 
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 5a776a08f78c..2da3316bb559 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -373,9 +373,23 @@ struct kvm_debugregs {
 	__u64 reserved[9];
 };
 
-/* for KVM_CAP_XSAVE */
+/* for KVM_CAP_XSAVE and KVM_CAP_XSAVE2 */
 struct kvm_xsave {
+	/*
+	 * KVM_GET_XSAVE2 and KVM_SET_XSAVE write and read as many bytes
+	 * as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+	 * respectively, when invoked on the vm file descriptor.
+	 *
+	 * The size value returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+	 * will always be at least 4096. Currently, it is only greater
+	 * than 4096 if a dynamic feature has been enabled with
+	 * ``arch_prctl()``, but this may change in the future.
+	 *
+	 * The offsets of the state save areas in struct kvm_xsave follow
+	 * the contents of CPUID leaf 0xD on the host.
+	 */
 	__u32 region[1024];
+	__u32 extra[0];
 };
 
 #define KVM_MAX_XCRS	16
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index ba4c3d5d2386..c55e57b30e81 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -32,7 +32,7 @@
 u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly;
 EXPORT_SYMBOL_GPL(kvm_cpu_caps);
 
-static u32 xstate_required_size(u64 xstate_bv, bool compacted)
+u32 xstate_required_size(u64 xstate_bv, bool compacted)
 {
 	int feature_bit = 0;
 	u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index c99edfff7f82..8a770b481d9d 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -30,6 +30,8 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
 bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 	       u32 *ecx, u32 *edx, bool exact_only);
 
+u32 xstate_required_size(u64 xstate_bv, bool compacted);
+
 int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu);
 u64 kvm_vcpu_reserved_gpa_bits_raw(struct kvm_vcpu *vcpu);
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 553e4af12edc..92a1ea13ad51 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4314,6 +4314,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		else
 			r = 0;
 		break;
+	case KVM_CAP_XSAVE2: {
+		u64 guest_perm = xstate_get_guest_group_perm();
+
+		r = xstate_required_size(supported_xcr0 & guest_perm, false);
+		if (r < sizeof(struct kvm_xsave))
+			r = sizeof(struct kvm_xsave);
+		break;
+	}
 	default:
 		break;
 	}
@@ -4917,6 +4925,16 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
 				       vcpu->arch.pkru);
 }
 
+static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
+					  u8 *state, unsigned int size)
+{
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
+		return;
+
+	fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
+				       state, size, vcpu->arch.pkru);
+}
+
 static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
 					struct kvm_xsave *guest_xsave)
 {
@@ -5370,6 +5388,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_GET_XSAVE: {
+		r = -EINVAL;
+		if (vcpu->arch.guest_fpu.uabi_size > sizeof(struct kvm_xsave))
+			break;
+
 		u.xsave = kzalloc(sizeof(struct kvm_xsave), GFP_KERNEL_ACCOUNT);
 		r = -ENOMEM;
 		if (!u.xsave)
@@ -5384,7 +5406,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_XSAVE: {
-		u.xsave = memdup_user(argp, sizeof(*u.xsave));
+		int size = vcpu->arch.guest_fpu.uabi_size;
+
+		u.xsave = memdup_user(argp, size);
 		if (IS_ERR(u.xsave)) {
 			r = PTR_ERR(u.xsave);
 			goto out_nofree;
@@ -5393,6 +5417,25 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = kvm_vcpu_ioctl_x86_set_xsave(vcpu, u.xsave);
 		break;
 	}
+
+	case KVM_GET_XSAVE2: {
+		int size = vcpu->arch.guest_fpu.uabi_size;
+
+		u.xsave = kzalloc(size, GFP_KERNEL_ACCOUNT);
+		r = -ENOMEM;
+		if (!u.xsave)
+			break;
+
+		kvm_vcpu_ioctl_x86_get_xsave2(vcpu, u.buffer, size);
+
+		r = -EFAULT;
+		if (copy_to_user(argp, u.xsave, size))
+			break;
+
+		r = 0;
+		break;
+	}
+
 	case KVM_GET_XCRS: {
 		u.xcrs = kzalloc(sizeof(struct kvm_xcrs), GFP_KERNEL_ACCOUNT);
 		r = -ENOMEM;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 12421e76adcb..6305426f1bc0 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
 #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
+#define KVM_CAP_XSAVE2 207
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1621,6 +1622,9 @@ struct kvm_enc_region {
 #define KVM_S390_NORMAL_RESET	_IO(KVMIO,   0xc3)
 #define KVM_S390_CLEAR_RESET	_IO(KVMIO,   0xc4)
 
+/* Available with KVM_CAP_XSAVE2 */
+#define KVM_GET_XSAVE2		  _IOR(KVMIO,  0xcf, struct kvm_xsave)
+
 struct kvm_s390_pv_sec_parm {
 	__u64 origin;
 	__u64 length;

[PATCH v5 19/21] kvm: selftests: Add support for KVM_CAP_XSAVE2

[Yang Zhong]

From: Wei Wang <wei.w.wang@intel.com>

When KVM_CAP_XSAVE2 is supported, userspace is expected to allocate
buffer for KVM_GET_XSAVE2 and KVM_SET_XSAVE using the size returned
by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Guang Zeng <guang.zeng@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 tools/arch/x86/include/uapi/asm/kvm.h         | 16 ++++-
 tools/include/uapi/linux/kvm.h                |  3 +
 .../testing/selftests/kvm/include/kvm_util.h  |  2 +
 .../selftests/kvm/include/x86_64/processor.h  | 10 +++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 32 +++++++++
 .../selftests/kvm/lib/x86_64/processor.c      | 67 ++++++++++++++++++-
 .../testing/selftests/kvm/x86_64/evmcs_test.c |  2 +-
 tools/testing/selftests/kvm/x86_64/smm_test.c |  2 +-
 .../testing/selftests/kvm/x86_64/state_test.c |  2 +-
 .../kvm/x86_64/vmx_preemption_timer_test.c    |  2 +-
 10 files changed, 130 insertions(+), 8 deletions(-)

diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
index 5a776a08f78c..2da3316bb559 100644
--- a/tools/arch/x86/include/uapi/asm/kvm.h
+++ b/tools/arch/x86/include/uapi/asm/kvm.h
@@ -373,9 +373,23 @@ struct kvm_debugregs {
 	__u64 reserved[9];
 };
 
-/* for KVM_CAP_XSAVE */
+/* for KVM_CAP_XSAVE and KVM_CAP_XSAVE2 */
 struct kvm_xsave {
+	/*
+	 * KVM_GET_XSAVE2 and KVM_SET_XSAVE write and read as many bytes
+	 * as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+	 * respectively, when invoked on the vm file descriptor.
+	 *
+	 * The size value returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+	 * will always be at least 4096. Currently, it is only greater
+	 * than 4096 if a dynamic feature has been enabled with
+	 * ``arch_prctl()``, but this may change in the future.
+	 *
+	 * The offsets of the state save areas in struct kvm_xsave follow
+	 * the contents of CPUID leaf 0xD on the host.
+	 */
 	__u32 region[1024];
+	__u32 extra[0];
 };
 
 #define KVM_MAX_XCRS	16
diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
index 1daa45268de2..f066637ee206 100644
--- a/tools/include/uapi/linux/kvm.h
+++ b/tools/include/uapi/linux/kvm.h
@@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
 #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
+#define KVM_CAP_XSAVE2 207
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1551,6 +1552,8 @@ struct kvm_s390_ucas_mapping {
 /* Available with KVM_CAP_XSAVE */
 #define KVM_GET_XSAVE		  _IOR(KVMIO,  0xa4, struct kvm_xsave)
 #define KVM_SET_XSAVE		  _IOW(KVMIO,  0xa5, struct kvm_xsave)
+/* Available with KVM_CAP_XSAVE2 */
+#define KVM_GET_XSAVE2		  _IOR(KVMIO,  0xcf, struct kvm_xsave)
 /* Available with KVM_CAP_XCRS */
 #define KVM_GET_XCRS		  _IOR(KVMIO,  0xa6, struct kvm_xcrs)
 #define KVM_SET_XCRS		  _IOW(KVMIO,  0xa7, struct kvm_xcrs)
diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 2d62edc49d67..65ace3f01fad 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -85,6 +85,7 @@ extern const struct vm_guest_mode_params vm_guest_mode_params[];
 int open_path_or_exit(const char *path, int flags);
 int open_kvm_dev_path_or_exit(void);
 int kvm_check_cap(long cap);
+int vm_check_cap(struct kvm_vm *vm, long cap);
 int vm_enable_cap(struct kvm_vm *vm, struct kvm_enable_cap *cap);
 int vcpu_enable_cap(struct kvm_vm *vm, uint32_t vcpu_id,
 		    struct kvm_enable_cap *cap);
@@ -316,6 +317,7 @@ struct kvm_vm *vm_create_with_vcpus(enum vm_guest_mode mode, uint32_t nr_vcpus,
  *   guest_code - The vCPU's entry point
  */
 void vm_vcpu_add_default(struct kvm_vm *vm, uint32_t vcpuid, void *guest_code);
+void vm_xsave_req_perm(void);
 
 bool vm_is_unrestricted_guest(struct kvm_vm *vm);
 
diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index 05e65ca1c30c..58633e51960f 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -10,8 +10,10 @@
 
 #include <assert.h>
 #include <stdint.h>
+#include <syscall.h>
 
 #include <asm/msr-index.h>
+#include <asm/prctl.h>
 
 #include "../kvm_util.h"
 
@@ -352,6 +354,7 @@ struct kvm_x86_state;
 struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid);
 void vcpu_load_state(struct kvm_vm *vm, uint32_t vcpuid,
 		     struct kvm_x86_state *state);
+void kvm_x86_state_cleanup(struct kvm_x86_state *state);
 
 struct kvm_msr_list *kvm_get_msr_index_list(void);
 uint64_t kvm_get_feature_msr(uint64_t msr_index);
@@ -443,4 +446,11 @@ void __virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr,
 /* VMX_EPT_VPID_CAP bits */
 #define VMX_EPT_VPID_CAP_AD_BITS       (1ULL << 21)
 
+#define XSTATE_XTILE_CFG_BIT		17
+#define XSTATE_XTILE_DATA_BIT		18
+
+#define XSTATE_XTILE_CFG_MASK		(1ULL << XSTATE_XTILE_CFG_BIT)
+#define XSTATE_XTILE_DATA_MASK		(1ULL << XSTATE_XTILE_DATA_BIT)
+#define XFEATURE_XTILE_MASK		(XSTATE_XTILE_CFG_MASK | \
+					XSTATE_XTILE_DATA_MASK)
 #endif /* SELFTEST_KVM_PROCESSOR_H */
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 53d2b5d04b82..318ac76fd2f1 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -85,6 +85,33 @@ int kvm_check_cap(long cap)
 	return ret;
 }
 
+/* VM Check Capability
+ *
+ * Input Args:
+ *   vm - Virtual Machine
+ *   cap - Capability
+ *
+ * Output Args: None
+ *
+ * Return:
+ *   On success, the Value corresponding to the capability (KVM_CAP_*)
+ *   specified by the value of cap.  On failure a TEST_ASSERT failure
+ *   is produced.
+ *
+ * Looks up and returns the value corresponding to the capability
+ * (KVM_CAP_*) given by cap.
+ */
+int vm_check_cap(struct kvm_vm *vm, long cap)
+{
+	int ret;
+
+	ret = ioctl(vm->fd, KVM_CHECK_EXTENSION, cap);
+	TEST_ASSERT(ret >= 0, "KVM_CHECK_EXTENSION VM IOCTL failed,\n"
+		"  rc: %i errno: %i", ret, errno);
+
+	return ret;
+}
+
 /* VM Enable Capability
  *
  * Input Args:
@@ -344,6 +371,11 @@ struct kvm_vm *vm_create_with_vcpus(enum vm_guest_mode mode, uint32_t nr_vcpus,
 	struct kvm_vm *vm;
 	int i;
 
+	/*
+	 * Permission needs to be requested before KVM_SET_CPUID2.
+	 */
+	vm_xsave_req_perm();
+
 	/* Force slot0 memory size not small than DEFAULT_GUEST_PHY_PAGES */
 	if (slot0_mem_pages < DEFAULT_GUEST_PHY_PAGES)
 		slot0_mem_pages = DEFAULT_GUEST_PHY_PAGES;
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index eef7b34756d5..f19d6d201977 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -650,6 +650,45 @@ static void vcpu_setup(struct kvm_vm *vm, int vcpuid)
 	vcpu_sregs_set(vm, vcpuid, &sregs);
 }
 
+#define CPUID_XFD_BIT (1 << 4)
+static bool is_xfd_supported(void)
+{
+	int eax, ebx, ecx, edx;
+	const int leaf = 0xd, subleaf = 0x1;
+
+	__asm__ __volatile__(
+		"cpuid"
+		: /* output */ "=a"(eax), "=b"(ebx),
+		  "=c"(ecx), "=d"(edx)
+		: /* input */ "0"(leaf), "2"(subleaf));
+
+	return !!(eax & CPUID_XFD_BIT);
+}
+
+void vm_xsave_req_perm(void)
+{
+	unsigned long bitmask;
+	long rc;
+
+	if (!is_xfd_supported())
+		return;
+
+	rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM,
+		     XSTATE_XTILE_DATA_BIT);
+	/*
+	 * The older kernel version(<5.15) can't support
+	 * ARCH_REQ_XCOMP_GUEST_PERM and directly return.
+	 */
+	if (rc)
+		return;
+
+	rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, &bitmask);
+	TEST_ASSERT(rc == 0, "prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld", rc);
+	TEST_ASSERT(bitmask & XFEATURE_XTILE_MASK,
+		    "prctl(ARCH_REQ_XCOMP_GUEST_PERM) failure bitmask=0x%lx",
+		    bitmask);
+}
+
 void vm_vcpu_add_default(struct kvm_vm *vm, uint32_t vcpuid, void *guest_code)
 {
 	struct kvm_mp_state mp_state;
@@ -1018,10 +1057,10 @@ void vcpu_dump(FILE *stream, struct kvm_vm *vm, uint32_t vcpuid, uint8_t indent)
 }
 
 struct kvm_x86_state {
+	struct kvm_xsave *xsave;
 	struct kvm_vcpu_events events;
 	struct kvm_mp_state mp_state;
 	struct kvm_regs regs;
-	struct kvm_xsave xsave;
 	struct kvm_xcrs xcrs;
 	struct kvm_sregs sregs;
 	struct kvm_debugregs debugregs;
@@ -1069,6 +1108,22 @@ struct kvm_msr_list *kvm_get_msr_index_list(void)
 	return list;
 }
 
+static int vcpu_save_xsave_state(struct kvm_vm *vm, struct vcpu *vcpu,
+				 struct kvm_x86_state *state)
+{
+	int size;
+
+	size = vm_check_cap(vm, KVM_CAP_XSAVE2);
+	if (!size)
+		size = sizeof(struct kvm_xsave);
+
+	state->xsave = malloc(size);
+	if (size == sizeof(struct kvm_xsave))
+		return ioctl(vcpu->fd, KVM_GET_XSAVE, state->xsave);
+	else
+		return ioctl(vcpu->fd, KVM_GET_XSAVE2, state->xsave);
+}
+
 struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid)
 {
 	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
@@ -1112,7 +1167,7 @@ struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid)
         TEST_ASSERT(r == 0, "Unexpected result from KVM_GET_REGS, r: %i",
                 r);
 
-	r = ioctl(vcpu->fd, KVM_GET_XSAVE, &state->xsave);
+	r = vcpu_save_xsave_state(vm, vcpu, state);
         TEST_ASSERT(r == 0, "Unexpected result from KVM_GET_XSAVE, r: %i",
                 r);
 
@@ -1157,7 +1212,7 @@ void vcpu_load_state(struct kvm_vm *vm, uint32_t vcpuid, struct kvm_x86_state *s
 	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
 	int r;
 
-	r = ioctl(vcpu->fd, KVM_SET_XSAVE, &state->xsave);
+	r = ioctl(vcpu->fd, KVM_SET_XSAVE, state->xsave);
         TEST_ASSERT(r == 0, "Unexpected result from KVM_SET_XSAVE, r: %i",
                 r);
 
@@ -1198,6 +1253,12 @@ void vcpu_load_state(struct kvm_vm *vm, uint32_t vcpuid, struct kvm_x86_state *s
 	}
 }
 
+void kvm_x86_state_cleanup(struct kvm_x86_state *state)
+{
+	free(state->xsave);
+	free(state);
+}
+
 bool is_intel_cpu(void)
 {
 	int eax, ebx, ecx, edx;
diff --git a/tools/testing/selftests/kvm/x86_64/evmcs_test.c b/tools/testing/selftests/kvm/x86_64/evmcs_test.c
index 2b46dcca86a8..4c7841dfd481 100644
--- a/tools/testing/selftests/kvm/x86_64/evmcs_test.c
+++ b/tools/testing/selftests/kvm/x86_64/evmcs_test.c
@@ -129,7 +129,7 @@ static void save_restore_vm(struct kvm_vm *vm)
 	vcpu_set_hv_cpuid(vm, VCPU_ID);
 	vcpu_enable_evmcs(vm, VCPU_ID);
 	vcpu_load_state(vm, VCPU_ID, state);
-	free(state);
+	kvm_x86_state_cleanup(state);
 
 	memset(&regs2, 0, sizeof(regs2));
 	vcpu_regs_get(vm, VCPU_ID, &regs2);
diff --git a/tools/testing/selftests/kvm/x86_64/smm_test.c b/tools/testing/selftests/kvm/x86_64/smm_test.c
index d0fe2fdce58c..2da8eb8e2d96 100644
--- a/tools/testing/selftests/kvm/x86_64/smm_test.c
+++ b/tools/testing/selftests/kvm/x86_64/smm_test.c
@@ -212,7 +212,7 @@ int main(int argc, char *argv[])
 		vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
 		vcpu_load_state(vm, VCPU_ID, state);
 		run = vcpu_state(vm, VCPU_ID);
-		free(state);
+		kvm_x86_state_cleanup(state);
 	}
 
 done:
diff --git a/tools/testing/selftests/kvm/x86_64/state_test.c b/tools/testing/selftests/kvm/x86_64/state_test.c
index 32854c1462ad..2e0a92da8ff5 100644
--- a/tools/testing/selftests/kvm/x86_64/state_test.c
+++ b/tools/testing/selftests/kvm/x86_64/state_test.c
@@ -218,7 +218,7 @@ int main(int argc, char *argv[])
 		vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
 		vcpu_load_state(vm, VCPU_ID, state);
 		run = vcpu_state(vm, VCPU_ID);
-		free(state);
+		kvm_x86_state_cleanup(state);
 
 		memset(&regs2, 0, sizeof(regs2));
 		vcpu_regs_get(vm, VCPU_ID, &regs2);
diff --git a/tools/testing/selftests/kvm/x86_64/vmx_preemption_timer_test.c b/tools/testing/selftests/kvm/x86_64/vmx_preemption_timer_test.c
index a07480aed397..ff92e25b6f1e 100644
--- a/tools/testing/selftests/kvm/x86_64/vmx_preemption_timer_test.c
+++ b/tools/testing/selftests/kvm/x86_64/vmx_preemption_timer_test.c
@@ -244,7 +244,7 @@ int main(int argc, char *argv[])
 		vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
 		vcpu_load_state(vm, VCPU_ID, state);
 		run = vcpu_state(vm, VCPU_ID);
-		free(state);
+		kvm_x86_state_cleanup(state);
 
 		memset(&regs2, 0, sizeof(regs2));
 		vcpu_regs_get(vm, VCPU_ID, &regs2);

[PATCH v5 20/21] x86/fpu: Provide fpu_sync_guest_vmexit_xfd_state()

[Yang Zhong]

From: Thomas Gleixner <tglx@linutronix.de>

KVM can disable the write emulation for the XFD MSR when the vCPU's fpstate
is already correctly sized to reduce the overhead.

When write emulation is disabled the XFD MSR state after a VMEXIT is
unknown and therefore not in sync with the software states in fpstate and
the per CPU XFD cache.

Provide fpu_sync_guest_vmexit_xfd_state() which has to be invoked after a
VMEXIT before enabling interrupts when write emulation is disabled for the
XFD MSR.

It could be invoked unconditionally even when write emulation is enabled
for the price of a pointless MSR read.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/fpu/api.h |  2 ++
 arch/x86/kernel/fpu/core.c     | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index e4d10155290b..a467eb80f9ed 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -142,8 +142,10 @@ extern int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatu
 
 #ifdef CONFIG_X86_64
 extern void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd);
+extern void fpu_sync_guest_vmexit_xfd_state(void);
 #else
 static inline void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd) { }
+static inline void fpu_sync_guest_vmexit_xfd_state(void) { }
 #endif
 
 extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 5e7de79c1fe1..e5dfd8b9825a 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -289,6 +289,30 @@ void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd)
 	fpregs_unlock();
 }
 EXPORT_SYMBOL_GPL(fpu_update_guest_xfd);
+
+/**
+ * fpu_sync_guest_vmexit_xfd_state - Synchronize XFD MSR and software state
+ *
+ * Must be invoked from KVM after a VMEXIT before enabling interrupts when
+ * XFD write emulation is disabled. This is required because the guest can
+ * freely modify XFD and the state at VMEXIT is not guaranteed to be the
+ * same as the state on VMENTER. So software state has to be udpated before
+ * any operation which depends on it can take place.
+ *
+ * Note: It can be invoked unconditionally even when write emulation is
+ * enabled for the price of a then pointless MSR read.
+ */
+void fpu_sync_guest_vmexit_xfd_state(void)
+{
+	struct fpstate *fps = current->thread.fpu.fpstate;
+
+	lockdep_assert_irqs_disabled();
+	if (fpu_state_size_dynamic()) {
+		rdmsrl(MSR_IA32_XFD, fps->xfd);
+		__this_cpu_write(xfd_state, fps->xfd);
+	}
+}
+EXPORT_SYMBOL_GPL(fpu_sync_guest_vmexit_xfd_state);
 #endif /* CONFIG_X86_64 */
 
 int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)

[PATCH v5 21/21] kvm: x86: Disable interception for IA32_XFD on demand

[Yang Zhong]

From: Kevin Tian <kevin.tian@intel.com>

Always intercepting IA32_XFD causes non-negligible overhead when this
register is updated frequently in the guest.

Disable r/w emulation after intercepting the first WRMSR(IA32_XFD)
with a non-zero value.

Disable WRMSR emulation implies that IA32_XFD becomes out-of-sync
with the software states in fpstate and the per-cpu xfd cache. This
leads to two additional changes accordingly:

  - Call fpu_sync_guest_vmexit_xfd_state() after vm-exit to bring
    software states back in-sync with the MSR, before handle_exit_irqoff()
    is called.

  - Always trap #NM once write interception is disabled for IA32_XFD.
    The #NM exception is rare if the guest doesn't use dynamic
    features. Otherwise, there is at most one exception per guest
    task given a dynamic feature.

p.s. We have confirmed that SDM is being revised to say that
when setting IA32_XFD[18] the AMX register state is not guaranteed
to be preserved. This clarification avoids adding mess for a creative
guest which sets IA32_XFD[18]=1 before saving active AMX state to
its own storage.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/vmx/vmx.c          | 24 +++++++++++++++++++-----
 arch/x86/kvm/vmx/vmx.h          |  2 +-
 arch/x86/kvm/x86.c              |  8 ++++++++
 4 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5d97f4adc1cb..2e8ffe269c23 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -647,6 +647,7 @@ struct kvm_vcpu_arch {
 	u64 smi_count;
 	bool tpr_access_reporting;
 	bool xsaves_enabled;
+	bool xfd_no_write_intercept;
 	u64 ia32_xss;
 	u64 microcode_version;
 	u64 arch_capabilities;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b601dc8a7f13..a3be4b02df2c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
 	MSR_FS_BASE,
 	MSR_GS_BASE,
 	MSR_KERNEL_GS_BASE,
+	MSR_IA32_XFD,
 	MSR_IA32_XFD_ERR,
 #endif
 	MSR_IA32_SYSENTER_CS,
@@ -764,10 +765,11 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu)
 	}
 
 	/*
-	 * Trap #NM if guest xfd contains a non-zero value so guest XFD_ERR
-	 * can be saved timely.
+	 * Disabling xfd interception indicates that dynamic xfeatures
+	 * might be used in the guest. Always trap #NM in this case
+	 * to save guest xfd_err timely.
 	 */
-	if (vcpu->arch.guest_fpu.fpstate->xfd)
+	if (vcpu->arch.xfd_no_write_intercept)
 		eb |= (1u << NM_VECTOR);
 
 	vmcs_write32(EXCEPTION_BITMAP, eb);
@@ -1978,9 +1980,21 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_XFD:
 		ret = kvm_set_msr_common(vcpu, msr_info);
-		/* Update #NM interception according to guest xfd */
-		if (!ret)
+		/*
+		 * Always intercepting WRMSR could incur non-negligible
+		 * overhead given xfd might be changed frequently in
+		 * guest context switch. Disable write interception
+		 * upon the first write with a non-zero value (indicating
+		 * potential usage on dynamic xfeatures). Also update
+		 * exception bitmap to trap #NM for proper virtualization
+		 * of guest xfd_err.
+		 */
+		if (!ret && data) {
+			vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD,
+						      MSR_TYPE_RW);
+			vcpu->arch.xfd_no_write_intercept = true;
 			vmx_update_exception_bitmap(vcpu);
+		}
 		break;
 #endif
 	case MSR_IA32_SYSENTER_CS:
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index e0922c80c9d1..7f2c82e7f38f 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -352,7 +352,7 @@ struct vcpu_vmx {
 	struct lbr_desc lbr_desc;
 
 	/* Save desired MSR intercept (read: pass-through) state */
-#define MAX_POSSIBLE_PASSTHROUGH_MSRS	14
+#define MAX_POSSIBLE_PASSTHROUGH_MSRS	15
 	struct {
 		DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
 		DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 92a1ea13ad51..df0150671b98 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10084,6 +10084,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	vcpu->mode = OUTSIDE_GUEST_MODE;
 	smp_wmb();
 
+	/*
+	 * Sync xfd before calling handle_exit_irqoff() which may
+	 * rely on the fact that guest_fpu::xfd is up-to-date (e.g.
+	 * in #NM irqoff handler).
+	 */
+	if (vcpu->arch.xfd_no_write_intercept)
+		fpu_sync_guest_vmexit_xfd_state();
+
 	static_call(kvm_x86_handle_exit_irqoff)(vcpu);
 
 	if (vcpu->arch.guest_fpu.xfd_err)

Re: [PATCH v5 07/21] x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM

[Paolo Bonzini]

On 1/5/22 13:35, Yang Zhong wrote:
> +int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures)
> +{
> +	lockdep_assert_preemption_enabled();
> +

The old fpu_update_guest_perm_features(guest_fpu) is equivalent to

	fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm);

Missing doc comment:

/*
  * fpu_enable_guest_xfd_features - Enable xfeatures according to guest perm
  * @guest_fpu:         Pointer to the guest FPU container
  * @xfeatures:         Features requested by guest CPUID
  *
  * Enable all dynamic xfeatures according to guest perm and requested CPUID.
  * Invoked if the caller wants to conservatively expand fpstate buffer instead
  * of waiting until XCR0 or XFD MSR is written.
  *
  * Return: 0 on success, error code otherwise
  */

Also, the check for 32-bit is slightly imprecise:

	/* Dynamic xfeatures are not supported with 32-bit kernels. */
	if (!IS_ENABLED(CONFIG_X86_64))
-		return 0;
+		return -EINVAL;

since we only get here with xfeatures != 0 (if it compiles, just removing
the IS_ENABLED check altogether would be even better).  With these changes,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo

Re: [PATCH v5 12/21] kvm: x86: Intercept #NM for saving IA32_XFD_ERR

[Sean Christopherson]

On Wed, Jan 05, 2022, Yang Zhong wrote:
> @@ -6399,6 +6424,26 @@ static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu,
>  	kvm_after_interrupt(vcpu);
>  }
>  
> +static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)
> +{
> +	/*
> +	 * Save xfd_err to guest_fpu before interrupt is enabled, so the
> +	 * MSR value is not clobbered by the host activity before the guest
> +	 * has chance to consume it.
> +	 *
> +	 * We should not blindly read xfd_err here, since this exception

Nit, avoid "we", and explain what KVM does (or doesn't) do, not what KVM "should"
do, e.g. just say

	 * Do not blindly read ...

> +	 * might be caused by L1 interception on a platform which doesn't
> +	 * support xfd at all.
> +	 *
> +	 * Do it conditionally upon guest_fpu::xfd. xfd_err matters
> +	 * only when xfd contains a non-zero value.
> +	 *
> +	 * Queuing exception is done in vmx_handle_exit. See comment there.

Another nit, it's worth explaining why XFD_ERR needs to be read here regardless
of is_guest_mode().  E.g.

	 * Injecting the #NM back into the guest is handled in the standard path
	 * as an #NM in L2 may be reflected into L1 as a VM-Exit.  Read XFD_ERR
	 * even if the #NM is from L2, as L1 may have exposed XFD to L2.

Side topic, in a follow up series/patch, it's probably worth adding support in
nested_vmx_prepare_msr_bitmap() to allow passthrough of the MSRs to L2.

> +	 */
> +	if (vcpu->arch.guest_fpu.fpstate->xfd)
> +		rdmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
> +}
> +
>  static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
>  {
>  	const unsigned long nmi_entry = (unsigned long)asm_exc_nmi_noist;
> @@ -6407,6 +6452,9 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
>  	/* if exit due to PF check for async PF */
>  	if (is_page_fault(intr_info))
>  		vmx->vcpu.arch.apf.host_apf_flags = kvm_read_and_reset_apf_flags();
> +	/* if exit due to NM, handle before interrupts are enabled */

Nit, drop this comment, it's slightly misleading since the #NM isn't fully handled
here.  The comment in handle_nm_fault_irqoff() is more than sufficient.

> +	else if (is_nm_fault(intr_info))
> +		handle_nm_fault_irqoff(&vmx->vcpu);
>  	/* Handle machine checks before interrupts are enabled */
>  	else if (is_machine_check(intr_info))
>  		kvm_machine_check();
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 21ce65220e38..2c988f8ca616 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9953,6 +9953,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	if (test_thread_flag(TIF_NEED_FPU_LOAD))
>  		switch_fpu_return();
>  
> +	if (vcpu->arch.guest_fpu.xfd_err)
> +		wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
> +
>  	if (unlikely(vcpu->arch.switch_db_regs)) {
>  		set_debugreg(0, 7);
>  		set_debugreg(vcpu->arch.eff_db[0], 0);
> @@ -10016,6 +10019,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  	static_call(kvm_x86_handle_exit_irqoff)(vcpu);
>  
> +	if (vcpu->arch.guest_fpu.xfd_err)
> +		wrmsrl(MSR_IA32_XFD_ERR, 0);
> +
>  	/*
>  	 * Consume any pending interrupts, including the possible source of
>  	 * VM-Exit on SVM and any ticks that occur between VM-Exit and now.

Re: [PATCH v5 16/21] kvm: x86: Add CPUID support for Intel AMX

[Sean Christopherson]

On Wed, Jan 05, 2022, Yang Zhong wrote:
> From: Jing Liu <jing2.liu@intel.com>
> 
> Extend CPUID emulation to support XFD, AMX_TILE, AMX_INT8 and
> AMX_BF16. Adding those bits into kvm_cpu_caps finally activates all
> previous logics in this series.
> 
> Hide XFD on 32bit host kernels. Otherwise it leads to a weird situation
> where KVM tells userspace to migrate MSR_IA32_XFD and then rejects
> attempts to read/write the MSR.
> 
> Signed-off-by: Jing Liu <jing2.liu@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

No need for my SoB, I provided a very tiny snippet of code review.

> Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> ---

Re: [PATCH v5 12/21] kvm: x86: Intercept #NM for saving IA32_XFD_ERR

[Jim Mattson]

On Wed, Jan 5, 2022 at 2:22 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Wed, Jan 05, 2022, Yang Zhong wrote:
> > @@ -6399,6 +6424,26 @@ static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu,
> >       kvm_after_interrupt(vcpu);
> >  }
> >
> > +static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)
> > +{
> > +     /*
> > +      * Save xfd_err to guest_fpu before interrupt is enabled, so the
> > +      * MSR value is not clobbered by the host activity before the guest
> > +      * has chance to consume it.
> > +      *
> > +      * We should not blindly read xfd_err here, since this exception
>
> Nit, avoid "we", and explain what KVM does (or doesn't) do, not what KVM "should"
> do, e.g. just say
>
>          * Do not blindly read ...
>
> > +      * might be caused by L1 interception on a platform which doesn't
> > +      * support xfd at all.
> > +      *
> > +      * Do it conditionally upon guest_fpu::xfd. xfd_err matters
> > +      * only when xfd contains a non-zero value.
> > +      *
> > +      * Queuing exception is done in vmx_handle_exit. See comment there.
>
> Another nit, it's worth explaining why XFD_ERR needs to be read here regardless
> of is_guest_mode().  E.g.
>
>          * Injecting the #NM back into the guest is handled in the standard path
>          * as an #NM in L2 may be reflected into L1 as a VM-Exit.  Read XFD_ERR
>          * even if the #NM is from L2, as L1 may have exposed XFD to L2.

Do we have tests of L1 passing through XFD to L2?

RE: [PATCH v5 07/21] x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM

[Tian, Kevin]

> From: Paolo Bonzini <pbonzini@redhat.com>
> Sent: Wednesday, January 5, 2022 9:07 PM
> 
> On 1/5/22 13:35, Yang Zhong wrote:
> > +int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64
> xfeatures)
> > +{
> > +	lockdep_assert_preemption_enabled();
> > +
> 
> The old fpu_update_guest_perm_features(guest_fpu) is equivalent to
> 
> 	fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm);
> 
> Missing doc comment:
> 
> /*
>   * fpu_enable_guest_xfd_features - Enable xfeatures according to guest
> perm
>   * @guest_fpu:         Pointer to the guest FPU container
>   * @xfeatures:         Features requested by guest CPUID
>   *
>   * Enable all dynamic xfeatures according to guest perm and requested
> CPUID.
>   * Invoked if the caller wants to conservatively expand fpstate buffer instead
>   * of waiting until XCR0 or XFD MSR is written.
>   *
>   * Return: 0 on success, error code otherwise
>   */

It's not equivalent. The old interface enables all xfeatures allowed by
guest perm while the new one just enables feature bits according to
the caller request. It also becomes a more general interface instead of
being only for conservative expansion. Since both points in the old
comment don't hold now and this function is obvious, we didn't put
a comment here (on par with other KVM helpers in that block).

If still necessary we could add one like below:

/*
  * fpu_enable_guest_xfd_features - Enable xfeatures for guest fpu container
  * @guest_fpu:         Pointer to the guest FPU container
  * @xfeatures:         Features requested by the caller
  *
  * Enable dynamic xfeatures and expand guest fpstate buffer accordingly.
  * KVM should call this function before the requested xfeatures are used
  * by the guest.
  *
  * Return: 0 on success, error code otherwise
  */

> 
> Also, the check for 32-bit is slightly imprecise:
> 
> 	/* Dynamic xfeatures are not supported with 32-bit kernels. */
> 	if (!IS_ENABLED(CONFIG_X86_64))
> -		return 0;
> +		return -EINVAL;
> 
> since we only get here with xfeatures != 0 (if it compiles, just removing
> the IS_ENABLED check altogether would be even better).  With these changes,
> 
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> Thanks,
> 
> Paolo

RE: [PATCH v5 16/21] kvm: x86: Add CPUID support for Intel AMX

[Tian, Kevin]

> From: Sean Christopherson <seanjc@google.com>
> Sent: Thursday, January 6, 2022 6:29 AM
> 
> On Wed, Jan 05, 2022, Yang Zhong wrote:
> > From: Jing Liu <jing2.liu@intel.com>
> >
> > Extend CPUID emulation to support XFD, AMX_TILE, AMX_INT8 and
> > AMX_BF16. Adding those bits into kvm_cpu_caps finally activates all
> > previous logics in this series.
> >
> > Hide XFD on 32bit host kernels. Otherwise it leads to a weird situation
> > where KVM tells userspace to migrate MSR_IA32_XFD and then rejects
> > attempts to read/write the MSR.
> >
> > Signed-off-by: Jing Liu <jing2.liu@intel.com>
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> 
> No need for my SoB, I provided a very tiny snippet of code review.
> 

It's not tiny if compared to the rest of the patch, but we certainly can
remove it. anyway thanks for all your suggestions which are all good. 😊

RE: [PATCH v5 12/21] kvm: x86: Intercept #NM for saving IA32_XFD_ERR

[Tian, Kevin]

> From: Sean Christopherson <seanjc@google.com>
> Sent: Thursday, January 6, 2022 6:22 AM
> 
> On Wed, Jan 05, 2022, Yang Zhong wrote:
> > @@ -6399,6 +6424,26 @@ static void handle_interrupt_nmi_irqoff(struct
> kvm_vcpu *vcpu,
> >  	kvm_after_interrupt(vcpu);
> >  }
> >
> > +static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)
> > +{
> > +	/*
> > +	 * Save xfd_err to guest_fpu before interrupt is enabled, so the
> > +	 * MSR value is not clobbered by the host activity before the guest
> > +	 * has chance to consume it.
> > +	 *
> > +	 * We should not blindly read xfd_err here, since this exception
> 
> Nit, avoid "we", and explain what KVM does (or doesn't) do, not what KVM
> "should"
> do, e.g. just say
> 
> 	 * Do not blindly read ...
> 
> > +	 * might be caused by L1 interception on a platform which doesn't
> > +	 * support xfd at all.
> > +	 *
> > +	 * Do it conditionally upon guest_fpu::xfd. xfd_err matters
> > +	 * only when xfd contains a non-zero value.
> > +	 *
> > +	 * Queuing exception is done in vmx_handle_exit. See comment
> there.
> 
> Another nit, it's worth explaining why XFD_ERR needs to be read here
> regardless
> of is_guest_mode().  E.g.
> 
> 	 * Injecting the #NM back into the guest is handled in the standard
> path
> 	 * as an #NM in L2 may be reflected into L1 as a VM-Exit.  Read
> XFD_ERR
> 	 * even if the #NM is from L2, as L1 may have exposed XFD to L2.

sounds good

> 
> Side topic, in a follow up series/patch, it's probably worth adding support in
> nested_vmx_prepare_msr_bitmap() to allow passthrough of the MSRs to L2.

will do.

> 
> > +	 */
> > +	if (vcpu->arch.guest_fpu.fpstate->xfd)
> > +		rdmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
> > +}
> > +
> >  static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
> >  {
> >  	const unsigned long nmi_entry = (unsigned long)asm_exc_nmi_noist;
> > @@ -6407,6 +6452,9 @@ static void handle_exception_nmi_irqoff(struct
> vcpu_vmx *vmx)
> >  	/* if exit due to PF check for async PF */
> >  	if (is_page_fault(intr_info))
> >  		vmx->vcpu.arch.apf.host_apf_flags =
> kvm_read_and_reset_apf_flags();
> > +	/* if exit due to NM, handle before interrupts are enabled */
> 
> Nit, drop this comment, it's slightly misleading since the #NM isn't fully
> handled
> here.  The comment in handle_nm_fault_irqoff() is more than sufficient.
> 
> > +	else if (is_nm_fault(intr_info))
> > +		handle_nm_fault_irqoff(&vmx->vcpu);
> >  	/* Handle machine checks before interrupts are enabled */
> >  	else if (is_machine_check(intr_info))
> >  		kvm_machine_check();
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 21ce65220e38..2c988f8ca616 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -9953,6 +9953,9 @@ static int vcpu_enter_guest(struct kvm_vcpu
> *vcpu)
> >  	if (test_thread_flag(TIF_NEED_FPU_LOAD))
> >  		switch_fpu_return();
> >
> > +	if (vcpu->arch.guest_fpu.xfd_err)
> > +		wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
> > +
> >  	if (unlikely(vcpu->arch.switch_db_regs)) {
> >  		set_debugreg(0, 7);
> >  		set_debugreg(vcpu->arch.eff_db[0], 0);
> > @@ -10016,6 +10019,9 @@ static int vcpu_enter_guest(struct kvm_vcpu
> *vcpu)
> >
> >  	static_call(kvm_x86_handle_exit_irqoff)(vcpu);
> >
> > +	if (vcpu->arch.guest_fpu.xfd_err)
> > +		wrmsrl(MSR_IA32_XFD_ERR, 0);
> > +
> >  	/*
> >  	 * Consume any pending interrupts, including the possible source of
> >  	 * VM-Exit on SVM and any ticks that occur between VM-Exit and
> now.

RE: [PATCH v5 12/21] kvm: x86: Intercept #NM for saving IA32_XFD_ERR

[Tian, Kevin]

> From: Jim Mattson <jmattson@google.com>
> Sent: Thursday, January 6, 2022 6:31 AM
> 
> On Wed, Jan 5, 2022 at 2:22 PM Sean Christopherson <seanjc@google.com>
> wrote:
> >
> > On Wed, Jan 05, 2022, Yang Zhong wrote:
> > > @@ -6399,6 +6424,26 @@ static void handle_interrupt_nmi_irqoff(struct
> kvm_vcpu *vcpu,
> > >       kvm_after_interrupt(vcpu);
> > >  }
> > >
> > > +static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)
> > > +{
> > > +     /*
> > > +      * Save xfd_err to guest_fpu before interrupt is enabled, so the
> > > +      * MSR value is not clobbered by the host activity before the guest
> > > +      * has chance to consume it.
> > > +      *
> > > +      * We should not blindly read xfd_err here, since this exception
> >
> > Nit, avoid "we", and explain what KVM does (or doesn't) do, not what KVM
> "should"
> > do, e.g. just say
> >
> >          * Do not blindly read ...
> >
> > > +      * might be caused by L1 interception on a platform which doesn't
> > > +      * support xfd at all.
> > > +      *
> > > +      * Do it conditionally upon guest_fpu::xfd. xfd_err matters
> > > +      * only when xfd contains a non-zero value.
> > > +      *
> > > +      * Queuing exception is done in vmx_handle_exit. See comment there.
> >
> > Another nit, it's worth explaining why XFD_ERR needs to be read here
> regardless
> > of is_guest_mode().  E.g.
> >
> >          * Injecting the #NM back into the guest is handled in the standard path
> >          * as an #NM in L2 may be reflected into L1 as a VM-Exit.  Read
> XFD_ERR
> >          * even if the #NM is from L2, as L1 may have exposed XFD to L2.
> 
> Do we have tests of L1 passing through XFD to L2?

As Sean mentioned passing through XFD to L2 still needs one more change
in nested_vmx_prepare_msr_bitmap(). This will be done in a follow-up patch.

btw we did verify having L1 emulate XFD for L2, by running the amx selftest
in L1. But overall nested configuration will need more test and polish after
this series.

Thanks
Kevin

Re: [PATCH v5 07/21] x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM

[Yang Zhong]

On Wed, Jan 05, 2022 at 02:06:40PM +0100, Paolo Bonzini wrote:
> On 1/5/22 13:35, Yang Zhong wrote:
> >+int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures)
> >+{
> >+	lockdep_assert_preemption_enabled();
> >+
> 
> The old fpu_update_guest_perm_features(guest_fpu) is equivalent to
> 
> 	fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm);
> 
> Missing doc comment:
> 
> /*
>  * fpu_enable_guest_xfd_features - Enable xfeatures according to guest perm
>  * @guest_fpu:         Pointer to the guest FPU container
>  * @xfeatures:         Features requested by guest CPUID
>  *
>  * Enable all dynamic xfeatures according to guest perm and requested CPUID.
>  * Invoked if the caller wants to conservatively expand fpstate buffer instead
>  * of waiting until XCR0 or XFD MSR is written.
>  *
>  * Return: 0 on success, error code otherwise
>  */
> 
> Also, the check for 32-bit is slightly imprecise:
> 
> 	/* Dynamic xfeatures are not supported with 32-bit kernels. */
> 	if (!IS_ENABLED(CONFIG_X86_64))
> -		return 0;
> +		return -EINVAL;
> 
> since we only get here with xfeatures != 0 (if it compiles, just removing
> the IS_ENABLED check altogether would be even better).  With these changes,
> 

  Paolo, I did 32 bit kernel build tests

  (1). w/ IS_ENABLED(CONFIG_X86_64)

      if (!IS_ENABLED(CONFIG_X86_64))
      	return -EINVAL; 
    
     This 32 bit kernel can successfully build.

  (2). remove IS_ENABLED(CONFIG_X86_64)

      The 32 bit kernel build is failed, and the error as:

      ld: arch/x86/kernel/fpu/core.o: in function `fpu_enable_guest_xfd_features':
/root/amx/v5/kvm/arch/x86/kernel/fpu/core.c:278: undefined reference to `__xfd_enable_feature'

      Seems we need define 32 bit API for __xfd_enable_feature().

   I also tried (1) in desktop, but I could not reboot the machine after installed 32 bit kernel.

   thanks a lot!

   Yang 





> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> Thanks,
> 
> Paolo