[patch 0/4] x86/fpu/kvm: Sanitize the FPU guest/user handling

[patch 0/4] x86/fpu/kvm: Sanitize the FPU guest/user handling

[Thomas Gleixner]

Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes also the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

The following series cleans that up and replaces the current scheme with a
single guest state which is switched in when entering vcpu_run() and
switched out before leaving it.

The rework is valuable even without AMX/XFD because it consumes less memory
and when swapping the fpstates there is no memory copy required when
TIF_NEED_LOAD_FPU is set on the going out fpstate.

The series is based on:

  git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/fpu-3

and is now part of the full AMX series:

  git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/fpu

On top of that I've integrated the KVM reallocation mechanism into:

  git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/fpu-kvm

The latter builds, boots and runs KVM guests, but that reallocation
functionality is obviously completely untested. I want to share this with
KVM folks so they can start to look how to integrate their XFD/XCR0 and
reallocation scheme as discussed and outlined here:

   https://lore.kernel.org/r/87mtn93u58.ffs@tglx

and the related thread. It's a tiny incremental update on top of x86/fpu (6
files changed, 183 insertions(+), 36 deletions(-)) which reuses the host
side mechanisms.

Thanks,

	tglx
---
 include/asm/fpu/api.h   |   19 ++++++--
 include/asm/fpu/types.h |   44 ++++++++++++++++++-
 include/asm/kvm_host.h  |    7 ---
 kernel/fpu/core.c       |  110 +++++++++++++++++++++++++++++++++---------------
 kvm/svm/svm.c           |    7 +--
 kvm/x86.c               |   88 ++++++++++----------------------------
 6 files changed, 165 insertions(+), 110 deletions(-)

[patch 1/4] x86/fpu: Prepare for sanitizing KVM FPU code

[Thomas Gleixner]

For the upcoming AMX support it's necessary to do a proper integration with
KVM. To avoid more nasty hackery in KVM which violate encapsulation extend
struct fpu and fpstate so the fpstate switching can be consolidated and
simplified.

Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Add fpu::__task_fpstate to save the regular fpstate pointer while the task
is inside vcpu_run(). Add some state fields to fpstate to indicate the
nature of the state.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/include/asm/fpu/types.h | 44 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)
---
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index b0cf6b75e467..81a01de1fec2 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -322,8 +322,32 @@ struct fpstate {
 	/* @user_xfeatures:	xfeatures valid in UABI buffers */
 	u64			user_xfeatures;
 
+	/* @is_valloc:		Indicator for dynamically allocated state */
+	unsigned int		is_valloc	: 1;
+
+	/* @is_guest:		Indicator for guest state (KVM) */
+	unsigned int		is_guest	: 1;
+
+	/*
+	 * @is_confidential:	Indicator for KVM confidential mode.
+	 *			The FPU registers are restored by the
+	 *			vmentry firmware from encrypted guest
+	 *			memory. On vmexit the FPU registers are
+	 *			saved by firmware to encrypted guest memory
+	 *			and the registers are scrubbed before
+	 *			returning to the host. So there is no
+	 *			content which is worth saving and restoring
+	 *			The fpstate has to be there so that
+	 *			preemption and softirq FPU usage works.
+	 *			without special casing.
+	 */
+	unsigned int		is_confidential	: 1;
+
+	/* @in_use:		State is in use */
+	unsigned int		in_use		: 1;
+
 	/* @regs: The register state union for all supported formats */
-	union fpregs_state		regs;
+	union fpregs_state	regs;
 
 	/* @regs is dynamically sized! Don't add anything after @regs! */
 } __attribute__ ((aligned (64)));
@@ -364,6 +388,14 @@ struct fpu {
 	struct fpstate			*fpstate;
 
 	/*
+	 * @__task_fpstate:
+	 *
+	 * Pointer to an inactive struct fpstate. Initialized to NULL. Is
+	 * used only for KVM support to swap out the regular task fpstate.
+	 */
+	struct fpstate			*__task_fpstate;
+
+	/*
 	 * @__fpstate:
 	 *
 	 * Initial in-memory storage for FPU registers which are saved in
@@ -379,6 +411,16 @@ struct fpu {
 };
 
 /*
+ * Guest pseudo FPU container
+ */
+struct fpu_guest {
+	/*
+	 * @fpstate:			Pointer to the allocated guest fpstate
+	 */
+	struct fpstate			*fpstate;
+};
+
+/*
  * FPU state configuration data. Initialized at boot time. Read only after init.
  */
 struct fpu_state_config {

[patch 2/4] x86/fpu: Provide infrastructure for KVM FPU cleanup

[Thomas Gleixner]

For the upcoming AMX support it's necessary to do a proper integration with
KVM. Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Provide:

  - An allocator which initializes the state properly

  - A replacement for the existing FPU swap mechanim

Aside of the reduced memory foot print, this also makes state switching
more efficient when TIF_FPU_NEED_LOAD is set. It does not require a memcpy
as the state is already correct in the to be swapped out fpstate.

The existing interfaces will be removed once KVM is converted over.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/include/asm/fpu/api.h | 13 ++++++-
 arch/x86/kernel/fpu/core.c     | 88 ++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 95 insertions(+), 6 deletions(-)
---
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 9ce83148058f..3b018140b3ae 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -135,9 +135,22 @@ extern void fpu_init_fpstate_user(struct fpu *fpu);
 extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
 
 /* KVM specific functions */
+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, u64 restore_mask);
 extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
 
 extern int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0, u32 *pkru);
 extern void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf, unsigned int size, u32 pkru);
 
+static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
+{
+	gfpu->fpstate->is_confidential = true;
+}
+
+static inline bool fpstate_is_confidential(struct fpu_guest *gfpu)
+{
+	return gfpu->fpstate->is_confidential;
+}
+
 #endif /* _ASM_X86_FPU_API_H */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index c23574905a33..d4c16bb37144 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -176,6 +176,78 @@ void fpu_reset_from_exception_fixup(void)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
+static void __fpstate_reset(struct fpstate *fpstate);
+
+bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
+{
+	struct fpstate *fpstate;
+	unsigned int size;
+
+	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+	fpstate = vzalloc(size);
+	if (!fpstate)
+		return false;
+
+	__fpstate_reset(fpstate);
+	fpstate_init_user(fpstate);
+	fpstate->is_valloc	= true;
+	fpstate->is_guest	= true;
+
+	gfpu->fpstate = fpstate;
+	return true;
+}
+EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);
+
+void fpu_free_guest_fpstate(struct fpu_guest *gfpu)
+{
+	struct fpstate *fps = gfpu->fpstate;
+
+	if (!fps)
+		return;
+
+	if (WARN_ON_ONCE(!fps->is_valloc || !fps->is_guest || fps->in_use))
+		return;
+
+	gfpu->fpstate = NULL;
+	vfree(fps);
+}
+EXPORT_SYMBOL_GPL(fpu_free_guest_fpstate);
+
+int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest,
+			 u64 restore_mask)
+{
+	struct fpstate *guest_fps = guest_fpu->fpstate;
+	struct fpu *fpu = &current->thread.fpu;
+	struct fpstate *cur_fps = fpu->fpstate;
+
+	fpregs_lock();
+	if (!cur_fps->is_confidential && !test_thread_flag(TIF_NEED_FPU_LOAD))
+		save_fpregs_to_fpstate(fpu);
+
+	/* Swap fpstate */
+	if (enter_guest) {
+		fpu->__task_fpstate = cur_fps;
+		fpu->fpstate = guest_fps;
+		guest_fps->in_use = true;
+	} else {
+		guest_fps->in_use = false;
+		fpu->fpstate = fpu->__task_fpstate;
+		fpu->__task_fpstate = NULL;
+	}
+
+	cur_fps = fpu->fpstate;
+
+	if (!cur_fps->is_confidential) {
+		restore_mask &= XFEATURE_MASK_FPSTATE;
+		restore_fpregs_from_fpstate(cur_fps, restore_mask);
+	}
+
+	fpregs_mark_activate();
+	fpregs_unlock();
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
+
 void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
 {
 	fpregs_lock();
@@ -352,16 +424,20 @@ void fpstate_init_user(struct fpstate *fpstate)
 		fpstate_init_fstate(fpstate);
 }
 
+static void __fpstate_reset(struct fpstate *fpstate)
+{
+	/* 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;
+}
+
 void fpstate_reset(struct fpu *fpu)
 {
 	/* Set the fpstate pointer to the default fpstate */
 	fpu->fpstate = &fpu->__fpstate;
-
-	/* Initialize sizes and feature masks */
-	fpu->fpstate->size		= fpu_kernel_cfg.default_size;
-	fpu->fpstate->user_size		= fpu_user_cfg.default_size;
-	fpu->fpstate->xfeatures		= fpu_kernel_cfg.default_features;
-	fpu->fpstate->user_xfeatures	= fpu_user_cfg.default_features;
+	__fpstate_reset(fpu->fpstate);
 }
 
 #if IS_ENABLED(CONFIG_KVM)

[patch 3/4] x86/kvm: Convert FPU handling to a single swap buffer

[Thomas Gleixner]

For the upcoming AMX support it's necessary to do a proper integration with
KVM. Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Convert the KVM FPU code over to this new scheme.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/include/asm/fpu/api.h  |  4 +-
 arch/x86/include/asm/kvm_host.h |  7 +---
 arch/x86/kernel/fpu/core.c      | 16 ++++----
 arch/x86/kvm/svm/svm.c          |  7 +--
 arch/x86/kvm/x86.c              | 88 +++++++++++-------------------------------
 5 files changed, 40 insertions(+), 82 deletions(-)
---
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 3b018140b3ae..239909a95368 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -140,8 +140,8 @@ extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
 extern int fpu_swap_kvm_fpstate(struct fpu_guest *gfpu, bool enter_guest, u64 restore_mask);
 extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
 
-extern int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0, u32 *pkru);
-extern void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf, unsigned int size, u32 pkru);
+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);
 
 static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
 {
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f8f48a7ec577..eb0d69bb2fc6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -691,11 +691,10 @@ struct kvm_vcpu_arch {
 	 *
 	 * Note that while the PKRU state lives inside the fpu registers,
 	 * it is switched out separately at VMENTER and VMEXIT time. The
-	 * "guest_fpu" state here contains the guest FPU context, with the
+	 * "guest_fpstate" state here contains the guest FPU context, with the
 	 * host PRKU bits.
 	 */
-	struct fpu *user_fpu;
-	struct fpu *guest_fpu;
+	struct fpu_guest guest_fpu;
 
 	u64 xcr0;
 	u64 guest_supported_xcr0;
@@ -1685,8 +1684,6 @@ void kvm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
 int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
 		    int reason, bool has_error_code, u32 error_code);
 
-void kvm_free_guest_fpu(struct kvm_vcpu *vcpu);
-
 void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned long cr0);
 void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned long cr4);
 int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d4c16bb37144..60681dc8a725 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -271,10 +271,10 @@ void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
 }
 EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
 
-void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf,
-			       unsigned int size, u32 pkru)
+void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
+				    unsigned int size, u32 pkru)
 {
-	struct fpstate *kstate = fpu->fpstate;
+	struct fpstate *kstate = gfpu->fpstate;
 	union fpregs_state *ustate = buf;
 	struct membuf mb = { .p = buf, .left = size };
 
@@ -287,12 +287,12 @@ void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf,
 		ustate->xsave.header.xfeatures = XFEATURE_MASK_FPSSE;
 	}
 }
-EXPORT_SYMBOL_GPL(fpu_copy_fpstate_to_kvm_uabi);
+EXPORT_SYMBOL_GPL(fpu_copy_guest_fpstate_to_uabi);
 
-int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0,
-				 u32 *vpkru)
+int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
+				   u64 xcr0, u32 *vpkru)
 {
-	struct fpstate *kstate = fpu->fpstate;
+	struct fpstate *kstate = gfpu->fpstate;
 	const union fpregs_state *ustate = buf;
 	struct pkru_state *xpkru;
 	int ret;
@@ -323,7 +323,7 @@ int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0,
 	xstate_init_xcomp_bv(&kstate->regs.xsave, fpu_user_cfg.max_features);
 	return 0;
 }
-EXPORT_SYMBOL_GPL(fpu_copy_kvm_uabi_to_fpstate);
+EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate);
 #endif /* CONFIG_KVM */
 
 void kernel_fpu_begin_mask(unsigned int kfpu_mask)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 05e8d4d27969..d027e8473ace 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -36,6 +36,7 @@
 #include <asm/spec-ctrl.h>
 #include <asm/cpu_device_id.h>
 #include <asm/traps.h>
+#include <asm/fpu/api.h>
 
 #include <asm/virtext.h>
 #include "trace.h"
@@ -1346,10 +1347,10 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
 		/*
 		 * SEV-ES guests maintain an encrypted version of their FPU
 		 * state which is restored and saved on VMRUN and VMEXIT.
-		 * Free the fpu structure to prevent KVM from attempting to
-		 * access the FPU state.
+		 * Mark vcpu->arch.guest_fpu->fpstate as scratch so it won't
+		 * do xsave/xrstor on it.
 		 */
-		kvm_free_guest_fpu(vcpu);
+		fpstate_set_confidential(&vcpu->arch.guest_fpu);
 	}
 
 	err = avic_init_vcpu(svm);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f085371ddd12..df36c8c195b0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -295,8 +295,6 @@ u64 __read_mostly host_xcr0;
 u64 __read_mostly supported_xcr0;
 EXPORT_SYMBOL_GPL(supported_xcr0);
 
-static struct kmem_cache *x86_fpu_cache;
-
 static struct kmem_cache *x86_emulator_cache;
 
 /*
@@ -4698,23 +4696,24 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
 					 struct kvm_xsave *guest_xsave)
 {
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return;
 
-	fpu_copy_fpstate_to_kvm_uabi(vcpu->arch.guest_fpu, guest_xsave->region,
-				     sizeof(guest_xsave->region),
-				     vcpu->arch.pkru);
+	fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
+				       guest_xsave->region,
+				       sizeof(guest_xsave->region),
+				       vcpu->arch.pkru);
 }
 
 static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
 					struct kvm_xsave *guest_xsave)
 {
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return 0;
 
-	return fpu_copy_kvm_uabi_to_fpstate(vcpu->arch.guest_fpu,
-					    guest_xsave->region,
-					    supported_xcr0, &vcpu->arch.pkru);
+	return fpu_copy_uabi_to_guest_fpstate(&vcpu->arch.guest_fpu,
+					      guest_xsave->region,
+					      supported_xcr0, &vcpu->arch.pkru);
 }
 
 static void kvm_vcpu_ioctl_x86_get_xcrs(struct kvm_vcpu *vcpu,
@@ -8287,18 +8286,11 @@ int kvm_arch_init(void *opaque)
 	}
 
 	r = -ENOMEM;
-	x86_fpu_cache = kmem_cache_create("x86_fpu", sizeof(struct fpu),
-					  __alignof__(struct fpu), SLAB_ACCOUNT,
-					  NULL);
-	if (!x86_fpu_cache) {
-		printk(KERN_ERR "kvm: failed to allocate cache for x86 fpu\n");
-		goto out;
-	}
 
 	x86_emulator_cache = kvm_alloc_emulator_cache();
 	if (!x86_emulator_cache) {
 		pr_err("kvm: failed to allocate cache for x86 emulator\n");
-		goto out_free_x86_fpu_cache;
+		goto out;
 	}
 
 	user_return_msrs = alloc_percpu(struct kvm_user_return_msrs);
@@ -8336,8 +8328,6 @@ int kvm_arch_init(void *opaque)
 	free_percpu(user_return_msrs);
 out_free_x86_emulator_cache:
 	kmem_cache_destroy(x86_emulator_cache);
-out_free_x86_fpu_cache:
-	kmem_cache_destroy(x86_fpu_cache);
 out:
 	return r;
 }
@@ -8364,7 +8354,6 @@ void kvm_arch_exit(void)
 	kvm_mmu_module_exit();
 	free_percpu(user_return_msrs);
 	kmem_cache_destroy(x86_emulator_cache);
-	kmem_cache_destroy(x86_fpu_cache);
 #ifdef CONFIG_KVM_XEN
 	static_key_deferred_flush(&kvm_xen_enabled);
 	WARN_ON(static_branch_unlikely(&kvm_xen_enabled.key));
@@ -9787,23 +9776,17 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
 {
 	/*
-	 * Guests with protected state have guest_fpu == NULL which makes
-	 * the swap only save the host state. Exclude PKRU from restore as
-	 * it is restored separately in kvm_x86_ops.run().
+	 * Exclude PKRU from restore as restored separately in
+	 * kvm_x86_ops.run().
 	 */
-	fpu_swap_kvm_fpu(vcpu->arch.user_fpu, vcpu->arch.guest_fpu,
-			 ~XFEATURE_MASK_PKRU);
+	fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, true, ~XFEATURE_MASK_PKRU);
 	trace_kvm_fpu(1);
 }
 
 /* When vcpu_run ends, restore user space FPU context. */
 static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 {
-	/*
-	 * Guests with protected state have guest_fpu == NULL which makes
-	 * swap only restore the host state.
-	 */
-	fpu_swap_kvm_fpu(vcpu->arch.guest_fpu, vcpu->arch.user_fpu, ~0ULL);
+	fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, false, ~0ULL);
 	++vcpu->stat.fpu_reload;
 	trace_kvm_fpu(0);
 }
@@ -10384,12 +10367,12 @@ int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
 	struct fxregs_state *fxsave;
 
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return 0;
 
 	vcpu_load(vcpu);
 
-	fxsave = &vcpu->arch.guest_fpu->fpstate->regs.fxsave;
+	fxsave = &vcpu->arch.guest_fpu.fpstate->regs.fxsave;
 	memcpy(fpu->fpr, fxsave->st_space, 128);
 	fpu->fcw = fxsave->cwd;
 	fpu->fsw = fxsave->swd;
@@ -10407,12 +10390,12 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
 	struct fxregs_state *fxsave;
 
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return 0;
 
 	vcpu_load(vcpu);
 
-	fxsave = &vcpu->arch.guest_fpu->fpstate->regs.fxsave;
+	fxsave = &vcpu->arch.guest_fpu.fpstate->regs.fxsave;
 
 	memcpy(fxsave->st_space, fpu->fpr, 128);
 	fxsave->cwd = fpu->fcw;
@@ -10473,15 +10456,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
 	vcpu->arch.cr0 |= X86_CR0_ET;
 }
 
-void kvm_free_guest_fpu(struct kvm_vcpu *vcpu)
-{
-	if (vcpu->arch.guest_fpu) {
-		kmem_cache_free(x86_fpu_cache, vcpu->arch.guest_fpu);
-		vcpu->arch.guest_fpu = NULL;
-	}
-}
-EXPORT_SYMBOL_GPL(kvm_free_guest_fpu);
-
 int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
 {
 	if (kvm_check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
@@ -10536,22 +10510,11 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	if (!alloc_emulate_ctxt(vcpu))
 		goto free_wbinvd_dirty_mask;
 
-	vcpu->arch.user_fpu = kmem_cache_zalloc(x86_fpu_cache,
-						GFP_KERNEL_ACCOUNT);
-	if (!vcpu->arch.user_fpu) {
-		pr_err("kvm: failed to allocate userspace's fpu\n");
-		goto free_emulate_ctxt;
-	}
-
-	vcpu->arch.guest_fpu = kmem_cache_zalloc(x86_fpu_cache,
-						 GFP_KERNEL_ACCOUNT);
-	if (!vcpu->arch.guest_fpu) {
+	if (!fpu_alloc_guest_fpstate(&vcpu->arch.guest_fpu)) {
 		pr_err("kvm: failed to allocate vcpu's fpu\n");
-		goto free_user_fpu;
+		goto free_emulate_ctxt;
 	}
 
-	fpu_init_fpstate_user(vcpu->arch.user_fpu);
-	fpu_init_fpstate_user(vcpu->arch.guest_fpu);
 	fx_init(vcpu);
 
 	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
@@ -10584,9 +10547,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	return 0;
 
 free_guest_fpu:
-	kvm_free_guest_fpu(vcpu);
-free_user_fpu:
-	kmem_cache_free(x86_fpu_cache, vcpu->arch.user_fpu);
+	fpu_free_guest_fpstate(&vcpu->arch.guest_fpu);
 free_emulate_ctxt:
 	kmem_cache_free(x86_emulator_cache, vcpu->arch.emulate_ctxt);
 free_wbinvd_dirty_mask:
@@ -10635,8 +10596,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 
 	kmem_cache_free(x86_emulator_cache, vcpu->arch.emulate_ctxt);
 	free_cpumask_var(vcpu->arch.wbinvd_dirty_mask);
-	kmem_cache_free(x86_fpu_cache, vcpu->arch.user_fpu);
-	kvm_free_guest_fpu(vcpu);
+	fpu_free_guest_fpstate(&vcpu->arch.guest_fpu);
 
 	kvm_hv_vcpu_uninit(vcpu);
 	kvm_pmu_destroy(vcpu);
@@ -10688,8 +10648,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	kvm_async_pf_hash_reset(vcpu);
 	vcpu->arch.apf.halted = false;
 
-	if (vcpu->arch.guest_fpu && kvm_mpx_supported()) {
-		struct fpstate *fpstate = vcpu->arch.guest_fpu->fpstate;
+	if (vcpu->arch.guest_fpu.fpstate && kvm_mpx_supported()) {
+		struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
 
 		/*
 		 * To avoid have the INIT path from kvm_apic_has_events() that be

[patch 4/4] x86/fpu: Remove old KVM FPU interface

[Thomas Gleixner]

No more users.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/include/asm/fpu/api.h |  2 --
 arch/x86/kernel/fpu/core.c     | 32 --------------------------------
 2 files changed, 34 deletions(-)
---
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 239909a95368..286a66ff0bd1 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -131,14 +131,12 @@ static inline void fpstate_init_soft(struct swregs_state *soft) {}
 DECLARE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
 /* fpstate-related functions which are exported to KVM */
-extern void fpu_init_fpstate_user(struct fpu *fpu);
 extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
 
 /* KVM specific functions */
 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, u64 restore_mask);
-extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
 
 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 60681dc8a725..4b09f0f70082 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -248,29 +248,6 @@ int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest,
 }
 EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
 
-void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
-{
-	fpregs_lock();
-
-	if (save) {
-		struct fpstate *fpcur = current->thread.fpu.fpstate;
-
-		if (test_thread_flag(TIF_NEED_FPU_LOAD))
-			memcpy(&save->fpstate->regs, &fpcur->regs, fpcur->size);
-		else
-			save_fpregs_to_fpstate(save);
-	}
-
-	if (rstor) {
-		restore_mask &= XFEATURE_MASK_FPSTATE;
-		restore_fpregs_from_fpstate(rstor->fpstate, restore_mask);
-	}
-
-	fpregs_mark_activate();
-	fpregs_unlock();
-}
-EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
-
 void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
 				    unsigned int size, u32 pkru)
 {
@@ -440,15 +417,6 @@ void fpstate_reset(struct fpu *fpu)
 	__fpstate_reset(fpu->fpstate);
 }
 
-#if IS_ENABLED(CONFIG_KVM)
-void fpu_init_fpstate_user(struct fpu *fpu)
-{
-	fpstate_reset(fpu);
-	fpstate_init_user(fpu->fpstate);
-}
-EXPORT_SYMBOL_GPL(fpu_init_fpstate_user);
-#endif
-
 /* Clone current's FPU state on fork */
 int fpu_clone(struct task_struct *dst)
 {

Re: [patch 3/4] x86/kvm: Convert FPU handling to a single swap buffer

[Paolo Bonzini]

On 17/10/21 19:03, Thomas Gleixner wrote:
>   	 */
> -	fpu_swap_kvm_fpu(vcpu->arch.user_fpu, vcpu->arch.guest_fpu,
> -			 ~XFEATURE_MASK_PKRU);
> +	fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, true, ~XFEATURE_MASK_PKRU);
>   	trace_kvm_fpu(1);
>   }
>   
>   /* When vcpu_run ends, restore user space FPU context. */
>   static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
>   {
> -	/*
> -	 * Guests with protected state have guest_fpu == NULL which makes
> -	 * swap only restore the host state.
> -	 */
> -	fpu_swap_kvm_fpu(vcpu->arch.guest_fpu, vcpu->arch.user_fpu, ~0ULL);
> +	fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, false, ~0ULL);

The restore mask can be ~XFEATURE_MASK_PKRU in this case tool this way 
it's constant and you can drop the third argument to the function.

Also perhaps it could be useful to add an

if (WARN_ON_ONCE(cur_fps->is_guest == enter_guest))
	return;

at the top of fpu_swap_kvm_fpstate, since the is_guest member (at least 
for now?) is only used for such kind of assertion.

Paolo

Re: [patch 0/4] x86/fpu/kvm: Sanitize the FPU guest/user handling

[Bae, Chang Seok]

On Oct 17, 2021, at 10:03, Thomas Gleixner <tglx@linutronix.de> wrote:
> 
> The latter builds, boots and runs KVM guests, but that reallocation
> functionality is obviously completely untested. 

Compiled and booted on bare-metal and KVM (guest with the same kernel).
No dmesg regression. No selftest regression.

Tested-by Chang S. Bae <chang.seok.bae@intel.com>

Thanks,
Chang

Re: [patch 0/4] x86/fpu/kvm: Sanitize the FPU guest/user handling

[Paolo Bonzini]

On 19/10/21 21:43, Bae, Chang Seok wrote:
> On Oct 17, 2021, at 10:03, Thomas Gleixner <tglx@linutronix.de> wrote:
>>
>> The latter builds, boots and runs KVM guests, but that reallocation
>> functionality is obviously completely untested.
> 
> Compiled and booted on bare-metal and KVM (guest with the same kernel).
> No dmesg regression. No selftest regression.
> 
> Tested-by Chang S. Bae <chang.seok.bae@intel.com>

Same here.  Thanks, Chang Seok!

Paolo