[PATCH v4 0/4] KVM: x86: MSR filtering and related fixes

[PATCH v4 0/4] KVM: x86: MSR filtering and related fixes

[Sean Christopherson]

Fix a nVMX MSR interception check bug, fix two intertwined nVMX bugs bugs
related to MSR filtering (one directly, one indirectly), and additional
cleanup on top.  The main SRCU fix from the original series was merged,
but these got left behind (luckily, becaues the main fix was buggy).

Side topic, getting a VM to actually barf on RDMSR(SPEC_CTRL) is comically
difficult: -spec-ctrl,-stibp,-ssbd,-ibrs-all,-ibpb,-amd-stibp,-amd-ssbd.
QEMU and KVM really, really want to expose SPEC_CTRL to the guest :-)

v4:
  - Rebase to 0d7d84498fb4 ("KVM: x86: SGX must obey the ... protocol")
  - Fix inverted passthrough check for SPEC_CTRL. [Vitaly] 
  - Add patch to fix MSR bitmap enabling check in helper.

v3:
  - Rebase to 9f6090b09d66 ("KVM: MMU: make spte .... in make_spte")

v2:
  - https://lkml.kernel.org/r/20210318224310.3274160-1-seanjc@google.com
  - Make the macro insanity slightly less insane. [Paolo]

v1: https://lkml.kernel.org/r/20210316184436.2544875-1-seanjc@google.com

Sean Christopherson (4):
  KVM: nVMX: Query current VMCS when determining if MSR bitmaps are in
    use
  KVM: nVMX: Handle dynamic MSR intercept toggling
  KVM: VMX: Macrofy the MSR bitmap getters and setters
  KVM: nVMX: Clean up x2APIC MSR handling for L2

 arch/x86/kvm/vmx/nested.c | 164 +++++++++++++++-----------------------
 arch/x86/kvm/vmx/vmx.c    |  61 ++------------
 arch/x86/kvm/vmx/vmx.h    |  28 +++++++
 3 files changed, 97 insertions(+), 156 deletions(-)

-- 
2.34.0.rc0.344.g81b53c2807-goog

[PATCH v4 1/4] KVM: nVMX: Query current VMCS when determining if MSR bitmaps are in use

[Sean Christopherson]

Check the current VMCS controls to determine if an MSR write will be
intercepted due to MSR bitmaps being disabled.  In the nested VMX case,
KVM will disable MSR bitmaps in vmcs02 if they're disabled in vmcs12 or
if KVM can't map L1's bitmaps for whatever reason.

Note, the bad behavior is relatively benign in the current code base as
KVM sets all bits in vmcs02's MSR bitmap by default, clears bits if and
only if L0 KVM also disables interception of an MSR, and only uses the
buggy helper for MSR_IA32_SPEC_CTRL.  Because KVM explicitly tests WRMSR
before disabling interception of MSR_IA32_SPEC_CTRL, the flawed check
will only result in KVM reading MSR_IA32_SPEC_CTRL from hardware when it
isn't strictly necessary.

Tag the fix for stable in case a future fix wants to use
msr_write_intercepted(), in which case a buggy implementation in older
kernels could prove subtly problematic.

Fixes: d28b387fb74d ("KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 71f54d85f104..334323bd787d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -769,15 +769,15 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu)
 /*
  * Check if MSR is intercepted for currently loaded MSR bitmap.
  */
-static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr)
+static bool msr_write_intercepted(struct vcpu_vmx *vmx, u32 msr)
 {
 	unsigned long *msr_bitmap;
 	int f = sizeof(unsigned long);
 
-	if (!cpu_has_vmx_msr_bitmap())
+	if (!(exec_controls_get(vmx) & CPU_BASED_USE_MSR_BITMAPS))
 		return true;
 
-	msr_bitmap = to_vmx(vcpu)->loaded_vmcs->msr_bitmap;
+	msr_bitmap = vmx->loaded_vmcs->msr_bitmap;
 
 	if (msr <= 0x1fff) {
 		return !!test_bit(msr, msr_bitmap + 0x800 / f);
@@ -6751,7 +6751,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	 * If the L02 MSR bitmap does not intercept the MSR, then we need to
 	 * save it.
 	 */
-	if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
+	if (unlikely(!msr_write_intercepted(vmx, MSR_IA32_SPEC_CTRL)))
 		vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
 	x86_spec_ctrl_restore_host(vmx->spec_ctrl, 0);
-- 
2.34.0.rc0.344.g81b53c2807-goog

[PATCH v4 2/4] KVM: nVMX: Handle dynamic MSR intercept toggling

[Sean Christopherson]

Always check vmcs01's MSR bitmap when merging L0 and L1 bitmaps for L2,
and always update the relevant bits in vmcs02.  This fixes two distinct,
but intertwined bugs related to dynamic MSR bitmap modifications.

The first issue is that KVM fails to enable MSR interception in vmcs02
for the FS/GS base MSRs if L1 first runs L2 with interception disabled,
and later enables interception.

The second issue is that KVM fails to honor userspace MSR filtering when
preparing vmcs02.

Fix both issues simultaneous as fixing only one of the issues (doesn't
matter which) would create a mess that no one should have to bisect.
Fixing only the first bug would exacerbate the MSR filtering issue as
userspace would see inconsistent behavior depending on the whims of L1.
Fixing only the second bug (MSR filtering) effectively requires fixing
the first, as the nVMX code only knows how to transition vmcs02's
bitmap from 1->0.

Move the various accessor/mutators that are currently buried in vmx.c
into vmx.h so that they can be shared by the nested code.

Fixes: 1a155254ff93 ("KVM: x86: Introduce MSR filtering")
Fixes: d69129b4e46a ("KVM: nVMX: Disable intercept for FS/GS base MSRs in vmcs02 when possible")
Cc: stable@vger.kernel.org
Cc: Alexander Graf <graf@amazon.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/nested.c | 111 +++++++++++++++++---------------------
 arch/x86/kvm/vmx/vmx.c    |  55 +------------------
 arch/x86/kvm/vmx/vmx.h    |  63 ++++++++++++++++++++++
 3 files changed, 115 insertions(+), 114 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index b4ee5e9f9e20..c569a135ca48 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -524,29 +524,6 @@ static int nested_vmx_check_tpr_shadow_controls(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
-/*
- * Check if MSR is intercepted for L01 MSR bitmap.
- */
-static bool msr_write_intercepted_l01(struct kvm_vcpu *vcpu, u32 msr)
-{
-	unsigned long *msr_bitmap;
-	int f = sizeof(unsigned long);
-
-	if (!cpu_has_vmx_msr_bitmap())
-		return true;
-
-	msr_bitmap = to_vmx(vcpu)->vmcs01.msr_bitmap;
-
-	if (msr <= 0x1fff) {
-		return !!test_bit(msr, msr_bitmap + 0x800 / f);
-	} else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff)) {
-		msr &= 0x1fff;
-		return !!test_bit(msr, msr_bitmap + 0xc00 / f);
-	}
-
-	return true;
-}
-
 /*
  * If a msr is allowed by L0, we should check whether it is allowed by L1.
  * The corresponding bit will be cleared unless both of L0 and L1 allow it.
@@ -600,6 +577,34 @@ static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap)
 	}
 }
 
+#define BUILD_NVMX_MSR_INTERCEPT_HELPER(rw)					\
+static inline									\
+void nested_vmx_set_msr_##rw##_intercept(struct vcpu_vmx *vmx,			\
+					 unsigned long *msr_bitmap_l1,		\
+					 unsigned long *msr_bitmap_l0, u32 msr)	\
+{										\
+	if (vmx_test_msr_bitmap_##rw(vmx->vmcs01.msr_bitmap, msr) ||		\
+	    vmx_test_msr_bitmap_##rw(msr_bitmap_l1, msr))			\
+		vmx_set_msr_bitmap_##rw(msr_bitmap_l0, msr);			\
+	else									\
+		vmx_clear_msr_bitmap_##rw(msr_bitmap_l0, msr);			\
+}
+BUILD_NVMX_MSR_INTERCEPT_HELPER(read)
+BUILD_NVMX_MSR_INTERCEPT_HELPER(write)
+
+static inline void nested_vmx_set_intercept_for_msr(struct vcpu_vmx *vmx,
+						    unsigned long *msr_bitmap_l1,
+						    unsigned long *msr_bitmap_l0,
+						    u32 msr, int types)
+{
+	if (types & MSR_TYPE_R)
+		nested_vmx_set_msr_read_intercept(vmx, msr_bitmap_l1,
+						  msr_bitmap_l0, msr);
+	if (types & MSR_TYPE_W)
+		nested_vmx_set_msr_write_intercept(vmx, msr_bitmap_l1,
+						   msr_bitmap_l0, msr);
+}
+
 /*
  * Merge L0's and L1's MSR bitmap, return false to indicate that
  * we do not use the hardware.
@@ -607,10 +612,11 @@ static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap)
 static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 						 struct vmcs12 *vmcs12)
 {
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	int msr;
 	unsigned long *msr_bitmap_l1;
-	unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.vmcs02.msr_bitmap;
-	struct kvm_host_map *map = &to_vmx(vcpu)->nested.msr_bitmap_map;
+	unsigned long *msr_bitmap_l0 = vmx->nested.vmcs02.msr_bitmap;
+	struct kvm_host_map *map = &vmx->nested.msr_bitmap_map;
 
 	/* Nothing to do if the MSR bitmap is not in use.  */
 	if (!cpu_has_vmx_msr_bitmap() ||
@@ -661,44 +667,27 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 		}
 	}
 
-	/* KVM unconditionally exposes the FS/GS base MSRs to L1. */
-#ifdef CONFIG_X86_64
-	nested_vmx_disable_intercept_for_msr(msr_bitmap_l1, msr_bitmap_l0,
-					     MSR_FS_BASE, MSR_TYPE_RW);
-
-	nested_vmx_disable_intercept_for_msr(msr_bitmap_l1, msr_bitmap_l0,
-					     MSR_GS_BASE, MSR_TYPE_RW);
-
-	nested_vmx_disable_intercept_for_msr(msr_bitmap_l1, msr_bitmap_l0,
-					     MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
-#endif
-
 	/*
-	 * Checking the L0->L1 bitmap is trying to verify two things:
-	 *
-	 * 1. L0 gave a permission to L1 to actually passthrough the MSR. This
-	 *    ensures that we do not accidentally generate an L02 MSR bitmap
-	 *    from the L12 MSR bitmap that is too permissive.
-	 * 2. That L1 or L2s have actually used the MSR. This avoids
-	 *    unnecessarily merging of the bitmap if the MSR is unused. This
-	 *    works properly because we only update the L01 MSR bitmap lazily.
-	 *    So even if L0 should pass L1 these MSRs, the L01 bitmap is only
-	 *    updated to reflect this when L1 (or its L2s) actually write to
-	 *    the MSR.
+	 * Always check vmcs01's bitmap to honor userspace MSR filters and any
+	 * other runtime changes to vmcs01's bitmap, e.g. dynamic pass-through.
 	 */
-	if (!msr_write_intercepted_l01(vcpu, MSR_IA32_SPEC_CTRL))
-		nested_vmx_disable_intercept_for_msr(
-					msr_bitmap_l1, msr_bitmap_l0,
-					MSR_IA32_SPEC_CTRL,
-					MSR_TYPE_R | MSR_TYPE_W);
-
-	if (!msr_write_intercepted_l01(vcpu, MSR_IA32_PRED_CMD))
-		nested_vmx_disable_intercept_for_msr(
-					msr_bitmap_l1, msr_bitmap_l0,
-					MSR_IA32_PRED_CMD,
-					MSR_TYPE_W);
-
-	kvm_vcpu_unmap(vcpu, &to_vmx(vcpu)->nested.msr_bitmap_map, false);
+#ifdef CONFIG_X86_64
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_FS_BASE, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_GS_BASE, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
+#endif
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_SPEC_CTRL, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_PRED_CMD, MSR_TYPE_W);
+
+	kvm_vcpu_unmap(vcpu, &vmx->nested.msr_bitmap_map, false);
 
 	return true;
 }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 334323bd787d..a0be26d3e81f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -771,22 +771,11 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu)
  */
 static bool msr_write_intercepted(struct vcpu_vmx *vmx, u32 msr)
 {
-	unsigned long *msr_bitmap;
-	int f = sizeof(unsigned long);
-
 	if (!(exec_controls_get(vmx) & CPU_BASED_USE_MSR_BITMAPS))
 		return true;
 
-	msr_bitmap = vmx->loaded_vmcs->msr_bitmap;
-
-	if (msr <= 0x1fff) {
-		return !!test_bit(msr, msr_bitmap + 0x800 / f);
-	} else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff)) {
-		msr &= 0x1fff;
-		return !!test_bit(msr, msr_bitmap + 0xc00 / f);
-	}
-
-	return true;
+	return vmx_test_msr_bitmap_write(vmx->loaded_vmcs->msr_bitmap,
+					 MSR_IA32_SPEC_CTRL);
 }
 
 static void clear_atomic_switch_msr_special(struct vcpu_vmx *vmx,
@@ -3697,46 +3686,6 @@ void free_vpid(int vpid)
 	spin_unlock(&vmx_vpid_lock);
 }
 
-static void vmx_clear_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__clear_bit(msr, msr_bitmap + 0x000 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__clear_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
-}
-
-static void vmx_clear_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__clear_bit(msr, msr_bitmap + 0x800 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__clear_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
-}
-
-static void vmx_set_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__set_bit(msr, msr_bitmap + 0x000 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__set_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
-}
-
-static void vmx_set_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__set_bit(msr, msr_bitmap + 0x800 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__set_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
-}
-
 void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index e7db42e3b0ce..d51311fa9ffc 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -400,6 +400,69 @@ static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
 
 void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
 
+static inline bool vmx_test_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
+{
+	int f = sizeof(unsigned long);
+
+	if (msr <= 0x1fff)
+		return test_bit(msr, msr_bitmap + 0x000 / f);
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
+		return test_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
+	return true;
+}
+
+static inline bool vmx_test_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
+{
+	int f = sizeof(unsigned long);
+
+	if (msr <= 0x1fff)
+		return test_bit(msr, msr_bitmap + 0x800 / f);
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
+		return test_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
+	return true;
+}
+
+static inline void vmx_clear_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
+{
+	int f = sizeof(unsigned long);
+
+	if (msr <= 0x1fff)
+		__clear_bit(msr, msr_bitmap + 0x000 / f);
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
+		__clear_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
+}
+
+static inline void vmx_clear_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
+{
+	int f = sizeof(unsigned long);
+
+	if (msr <= 0x1fff)
+		__clear_bit(msr, msr_bitmap + 0x800 / f);
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
+		__clear_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
+}
+
+static inline void vmx_set_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
+{
+	int f = sizeof(unsigned long);
+
+	if (msr <= 0x1fff)
+		__set_bit(msr, msr_bitmap + 0x000 / f);
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
+		__set_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
+}
+
+static inline void vmx_set_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
+{
+	int f = sizeof(unsigned long);
+
+	if (msr <= 0x1fff)
+		__set_bit(msr, msr_bitmap + 0x800 / f);
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
+		__set_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
+}
+
+
 static inline u8 vmx_get_rvi(void)
 {
 	return vmcs_read16(GUEST_INTR_STATUS) & 0xff;
-- 
2.34.0.rc0.344.g81b53c2807-goog

[PATCH v4 3/4] KVM: VMX: Macrofy the MSR bitmap getters and setters

[Sean Christopherson]

Add builder macros to generate the MSR bitmap helpers to reduce the
amount of copy-paste code, especially with respect to all the magic
numbers needed to calc the correct bit location.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.h | 77 ++++++++++--------------------------------
 1 file changed, 17 insertions(+), 60 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index d51311fa9ffc..83a14b61c80f 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -400,68 +400,25 @@ static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
 
 void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
 
-static inline bool vmx_test_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		return test_bit(msr, msr_bitmap + 0x000 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		return test_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
-	return true;
-}
-
-static inline bool vmx_test_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		return test_bit(msr, msr_bitmap + 0x800 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		return test_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
-	return true;
-}
-
-static inline void vmx_clear_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__clear_bit(msr, msr_bitmap + 0x000 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__clear_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
-}
-
-static inline void vmx_clear_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__clear_bit(msr, msr_bitmap + 0x800 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__clear_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
-}
-
-static inline void vmx_set_msr_bitmap_read(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__set_bit(msr, msr_bitmap + 0x000 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__set_bit(msr & 0x1fff, msr_bitmap + 0x400 / f);
-}
-
-static inline void vmx_set_msr_bitmap_write(ulong *msr_bitmap, u32 msr)
-{
-	int f = sizeof(unsigned long);
-
-	if (msr <= 0x1fff)
-		__set_bit(msr, msr_bitmap + 0x800 / f);
-	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))
-		__set_bit(msr & 0x1fff, msr_bitmap + 0xc00 / f);
+#define __BUILD_VMX_MSR_BITMAP_HELPER(rtype, action, bitop, access, base)      \
+static inline rtype vmx_##action##_msr_bitmap_##access(unsigned long *bitmap,  \
+						       u32 msr)		       \
+{									       \
+	int f = sizeof(unsigned long);					       \
+									       \
+	if (msr <= 0x1fff)						       \
+		return bitop##_bit(msr, bitmap + base / f);		       \
+	else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff))		       \
+		return bitop##_bit(msr & 0x1fff, bitmap + (base + 0x400) / f); \
+	return (rtype)true;						       \
 }
+#define BUILD_VMX_MSR_BITMAP_HELPERS(ret_type, action, bitop)		       \
+	__BUILD_VMX_MSR_BITMAP_HELPER(ret_type, action, bitop, read,  0x0)     \
+	__BUILD_VMX_MSR_BITMAP_HELPER(ret_type, action, bitop, write, 0x800)
 
+BUILD_VMX_MSR_BITMAP_HELPERS(bool, test, test)
+BUILD_VMX_MSR_BITMAP_HELPERS(void, clear, __clear)
+BUILD_VMX_MSR_BITMAP_HELPERS(void, set, __set)
 
 static inline u8 vmx_get_rvi(void)
 {
-- 
2.34.0.rc0.344.g81b53c2807-goog

[PATCH v4 4/4] KVM: nVMX: Clean up x2APIC MSR handling for L2

[Sean Christopherson]

Clean up the x2APIC MSR bitmap intereption code for L2, which is the last
holdout of open coded bitmap manipulations.  Freshen up the SDM/PRM
comment, rename the function to make it abundantly clear the funky
behavior is x2APIC specific, and explain _why_ vmcs01's bitmap is ignored
(the previous comment was flat out wrong for x2APIC behavior).

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/nested.c | 53 +++++++++++----------------------------
 arch/x86/kvm/vmx/vmx.h    |  8 ++++++
 2 files changed, 22 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index c569a135ca48..341c50816822 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -525,44 +525,19 @@ static int nested_vmx_check_tpr_shadow_controls(struct kvm_vcpu *vcpu,
 }
 
 /*
- * If a msr is allowed by L0, we should check whether it is allowed by L1.
- * The corresponding bit will be cleared unless both of L0 and L1 allow it.
+ * For x2APIC MSRs, ignore the vmcs01 bitmap.  L1 can enable x2APIC without L1
+ * itself utilizing x2APIC.  All MSRs were previously set to be intercepted,
+ * only the "disable intercept" case needs to be handled.
  */
-static void nested_vmx_disable_intercept_for_msr(unsigned long *msr_bitmap_l1,
-					       unsigned long *msr_bitmap_nested,
-					       u32 msr, int type)
+static void nested_vmx_disable_intercept_for_x2apic_msr(unsigned long *msr_bitmap_l1,
+							unsigned long *msr_bitmap_l0,
+							u32 msr, int type)
 {
-	int f = sizeof(unsigned long);
+	if (type & MSR_TYPE_R && !vmx_test_msr_bitmap_read(msr_bitmap_l1, msr))
+		vmx_clear_msr_bitmap_read(msr_bitmap_l0, msr);
 
-	/*
-	 * See Intel PRM Vol. 3, 20.6.9 (MSR-Bitmap Address). Early manuals
-	 * have the write-low and read-high bitmap offsets the wrong way round.
-	 * We can control MSRs 0x00000000-0x00001fff and 0xc0000000-0xc0001fff.
-	 */
-	if (msr <= 0x1fff) {
-		if (type & MSR_TYPE_R &&
-		   !test_bit(msr, msr_bitmap_l1 + 0x000 / f))
-			/* read-low */
-			__clear_bit(msr, msr_bitmap_nested + 0x000 / f);
-
-		if (type & MSR_TYPE_W &&
-		   !test_bit(msr, msr_bitmap_l1 + 0x800 / f))
-			/* write-low */
-			__clear_bit(msr, msr_bitmap_nested + 0x800 / f);
-
-	} else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff)) {
-		msr &= 0x1fff;
-		if (type & MSR_TYPE_R &&
-		   !test_bit(msr, msr_bitmap_l1 + 0x400 / f))
-			/* read-high */
-			__clear_bit(msr, msr_bitmap_nested + 0x400 / f);
-
-		if (type & MSR_TYPE_W &&
-		   !test_bit(msr, msr_bitmap_l1 + 0xc00 / f))
-			/* write-high */
-			__clear_bit(msr, msr_bitmap_nested + 0xc00 / f);
-
-	}
+	if (type & MSR_TYPE_W && !vmx_test_msr_bitmap_write(msr_bitmap_l1, msr))
+		vmx_clear_msr_bitmap_write(msr_bitmap_l0, msr);
 }
 
 static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap)
@@ -631,7 +606,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 	/*
 	 * To keep the control flow simple, pay eight 8-byte writes (sixteen
 	 * 4-byte writes on 32-bit systems) up front to enable intercepts for
-	 * the x2APIC MSR range and selectively disable them below.
+	 * the x2APIC MSR range and selectively toggle those relevant to L2.
 	 */
 	enable_x2apic_msr_intercepts(msr_bitmap_l0);
 
@@ -650,17 +625,17 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 			}
 		}
 
-		nested_vmx_disable_intercept_for_msr(
+		nested_vmx_disable_intercept_for_x2apic_msr(
 			msr_bitmap_l1, msr_bitmap_l0,
 			X2APIC_MSR(APIC_TASKPRI),
 			MSR_TYPE_R | MSR_TYPE_W);
 
 		if (nested_cpu_has_vid(vmcs12)) {
-			nested_vmx_disable_intercept_for_msr(
+			nested_vmx_disable_intercept_for_x2apic_msr(
 				msr_bitmap_l1, msr_bitmap_l0,
 				X2APIC_MSR(APIC_EOI),
 				MSR_TYPE_W);
-			nested_vmx_disable_intercept_for_msr(
+			nested_vmx_disable_intercept_for_x2apic_msr(
 				msr_bitmap_l1, msr_bitmap_l0,
 				X2APIC_MSR(APIC_SELF_IPI),
 				MSR_TYPE_W);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 83a14b61c80f..86c093da0d63 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -400,6 +400,14 @@ static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
 
 void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
 
+/*
+ * Note, early Intel manuals have the write-low and read-high bitmap offsets
+ * the wrong way round.  The bitmaps control MSRs 0x00000000-0x00001fff and
+ * 0xc0000000-0xc0001fff.  The former (low) uses bytes 0-0x3ff for reads and
+ * 0x800-0xbff for writes.  The latter (high) uses 0x400-0x7ff for reads and
+ * 0xc00-0xfff for writes.  MSRs not covered by either of the ranges always
+ * VM-Exit.
+ */
 #define __BUILD_VMX_MSR_BITMAP_HELPER(rtype, action, bitop, access, base)      \
 static inline rtype vmx_##action##_msr_bitmap_##access(unsigned long *bitmap,  \
 						       u32 msr)		       \
-- 
2.34.0.rc0.344.g81b53c2807-goog

Re: [PATCH v4 0/4] KVM: x86: MSR filtering and related fixes

[Paolo Bonzini]

On 11/9/21 02:30, Sean Christopherson wrote:
> Fix a nVMX MSR interception check bug, fix two intertwined nVMX bugs bugs
> related to MSR filtering (one directly, one indirectly), and additional
> cleanup on top.  The main SRCU fix from the original series was merged,
> but these got left behind (luckily, becaues the main fix was buggy).
> 
> Side topic, getting a VM to actually barf on RDMSR(SPEC_CTRL) is comically
> difficult: -spec-ctrl,-stibp,-ssbd,-ibrs-all,-ibpb,-amd-stibp,-amd-ssbd.
> QEMU and KVM really, really want to expose SPEC_CTRL to the guest :-)
> 
> v4:
>    - Rebase to 0d7d84498fb4 ("KVM: x86: SGX must obey the ... protocol")
>    - Fix inverted passthrough check for SPEC_CTRL. [Vitaly]
>    - Add patch to fix MSR bitmap enabling check in helper.
> 
> v3:
>    - Rebase to 9f6090b09d66 ("KVM: MMU: make spte .... in make_spte")
> 
> v2:
>    - https://lkml.kernel.org/r/20210318224310.3274160-1-seanjc@google.com
>    - Make the macro insanity slightly less insane. [Paolo]
> 
> v1: https://lkml.kernel.org/r/20210316184436.2544875-1-seanjc@google.com
> 
> Sean Christopherson (4):
>    KVM: nVMX: Query current VMCS when determining if MSR bitmaps are in
>      use
>    KVM: nVMX: Handle dynamic MSR intercept toggling
>    KVM: VMX: Macrofy the MSR bitmap getters and setters
>    KVM: nVMX: Clean up x2APIC MSR handling for L2
> 
>   arch/x86/kvm/vmx/nested.c | 164 +++++++++++++++-----------------------
>   arch/x86/kvm/vmx/vmx.c    |  61 ++------------
>   arch/x86/kvm/vmx/vmx.h    |  28 +++++++
>   3 files changed, 97 insertions(+), 156 deletions(-)
> 

Queued, thanks.

Paolo