[PATCH v4 0/8] KVM: nVMX: Enlightened MSR Bitmap feature for Hyper-V on KVM (+ KVM: x86: MSR filtering and related fixes)

[PATCH v4 0/8] KVM: nVMX: Enlightened MSR Bitmap feature for Hyper-V on KVM (+ KVM: x86: MSR filtering and related fixes)

[Vitaly Kuznetsov]

This series combines "Enlightened MSR Bitmap feature for Hyper-V on KVM v4"
and Sean's "KVM: x86: MSR filtering and related fixes v4" 
(https://lore.kernel.org/kvm/20211109013047.2041518-1-seanjc@google.com/)
series as they're code dependent.

Changes in "Enlightened MSR Bitmap feature for Hyper-V on KVM v4" since
 v3 [Sean]:
- Move Hyper-V Enlightened MSR Bitmap in vmx_create_vcpu() and expand
  the comment.
- Add R-b tag to "KVM: VMX: Introduce vmx_msr_bitmap_l01_changed() helper".
- s,msr_bitmap_force_recalc,force_msr_bitmap_recalc,
- Drop unneeded 'out_clear_msr_bitmap_force_recalc' path from "KVM: nVMX:
  Implement Enlightened MSR Bitmap feature".

Original description of the feature:

Updating MSR bitmap for L2 is not cheap and rearly needed. TLFS for Hyper-V
offers 'Enlightened MSR Bitmap' feature which allows L1 hypervisor to
inform L0 when it changes MSR bitmap, this eliminates the need to examine
L1's MSR bitmap for L2 every time when 'real' MSR bitmap for L2 gets
constructed.

When the feature is enabled for Win10+WSL2, it shaves off around 700 CPU
cycles from a nested vmexit cost (tight cpuid loop test).

First patch of the series is unrelated to the newly implemented feature,
it fixes a bug in Enlightened MSR Bitmap usage when KVM runs as a nested
hypervisor on top of Hyper-V.

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

Vitaly Kuznetsov (4):
  KVM: nVMX: Don't use Enlightened MSR Bitmap for L3
  KVM: VMX: Introduce vmx_msr_bitmap_l01_changed() helper
  KVM: nVMX: Track whether changes in L0 require MSR bitmap for L2 to be
    rebuilt
  KVM: nVMX: Implement Enlightened MSR Bitmap feature

 arch/x86/kvm/hyperv.c     |   2 +
 arch/x86/kvm/vmx/nested.c | 177 +++++++++++++++++---------------------
 arch/x86/kvm/vmx/vmx.c    |  94 +++++++-------------
 arch/x86/kvm/vmx/vmx.h    |  37 ++++++++
 4 files changed, 149 insertions(+), 161 deletions(-)

-- 
2.31.1

[PATCH v4 1/8] KVM: nVMX: Query current VMCS when determining if MSR bitmaps are in use

[Vitaly Kuznetsov]

From: Sean Christopherson <seanjc@google.com>

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>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.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);
-- 
2.31.1

[PATCH v4 2/8] KVM: nVMX: Handle dynamic MSR intercept toggling

[Vitaly Kuznetsov]

From: Sean Christopherson <seanjc@google.com>

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>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 103 +++++++++++++++++---------------------
 arch/x86/kvm/vmx/vmx.c    |  55 +-------------------
 arch/x86/kvm/vmx/vmx.h    |  63 +++++++++++++++++++++++
 3 files changed, 111 insertions(+), 110 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. */
+	/*
+	 * Always check vmcs01's bitmap to honor userspace MSR filters and any
+	 * other runtime changes to vmcs01's bitmap, e.g. dynamic pass-through.
+	 */
 #ifdef CONFIG_X86_64
-	nested_vmx_disable_intercept_for_msr(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_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_set_intercept_for_msr(vmx, 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);
+	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);
 
-	/*
-	 * 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.
-	 */
-	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);
+	nested_vmx_set_intercept_for_msr(vmx, 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);
+	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;
-- 
2.31.1

[PATCH v4 3/8] KVM: VMX: Macrofy the MSR bitmap getters and setters

[Vitaly Kuznetsov]

From: Sean Christopherson <seanjc@google.com>

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>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.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)
 {
-- 
2.31.1

[PATCH v4 4/8] KVM: nVMX: Clean up x2APIC MSR handling for L2

[Vitaly Kuznetsov]

From: Sean Christopherson <seanjc@google.com>

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>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.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)		       \
-- 
2.31.1

[PATCH v4 5/8] KVM: nVMX: Don't use Enlightened MSR Bitmap for L3

[Vitaly Kuznetsov]

When KVM runs as a nested hypervisor on top of Hyper-V it uses Enlightened
VMCS and enables Enlightened MSR Bitmap feature for its L1s and L2s (which
are actually L2s and L3s from Hyper-V's perspective). When MSR bitmap is
updated, KVM has to reset HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP from
clean fields to make Hyper-V aware of the change. For KVM's L1s, this is
done in vmx_disable_intercept_for_msr()/vmx_enable_intercept_for_msr().
MSR bitmap for L2 is build in nested_vmx_prepare_msr_bitmap() by blending
MSR bitmap for L1 and L1's idea of MSR bitmap for L2. KVM, however, doesn't
check if the resulting bitmap is different and never cleans
HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP in eVMCS02. This is incorrect and
may result in Hyper-V missing the update.

The issue could've been solved by calling evmcs_touch_msr_bitmap() for
eVMCS02 from nested_vmx_prepare_msr_bitmap() unconditionally but doing so
would not give any performance benefits (compared to not using Enlightened
MSR Bitmap at all). 3-level nesting is also not a very common setup
nowadays.

Don't enable 'Enlightened MSR Bitmap' feature for KVM's L2s (real L3s) for
now.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/vmx/vmx.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a0be26d3e81f..fc87b6bbd277 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2646,15 +2646,6 @@ int alloc_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
 		if (!loaded_vmcs->msr_bitmap)
 			goto out_vmcs;
 		memset(loaded_vmcs->msr_bitmap, 0xff, PAGE_SIZE);
-
-		if (IS_ENABLED(CONFIG_HYPERV) &&
-		    static_branch_unlikely(&enable_evmcs) &&
-		    (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) {
-			struct hv_enlightened_vmcs *evmcs =
-				(struct hv_enlightened_vmcs *)loaded_vmcs->vmcs;
-
-			evmcs->hv_enlightenments_control.msr_bitmap = 1;
-		}
 	}
 
 	memset(&loaded_vmcs->host_state, 0, sizeof(struct vmcs_host_state));
@@ -6831,6 +6822,19 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 	if (err < 0)
 		goto free_pml;
 
+	/*
+	 * Use Hyper-V 'Enlightened MSR Bitmap' feature when KVM runs as a
+	 * nested (L1) hypervisor and Hyper-V in L0 supports it. Enable the
+	 * feature only for vmcs01, KVM currently isn't equipped to realize any
+	 * performance benefits from enabling it for vmcs02.
+	 */
+	if (IS_ENABLED(CONFIG_HYPERV) && static_branch_unlikely(&enable_evmcs) &&
+	    (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) {
+		struct hv_enlightened_vmcs *evmcs = (void *)vmx->vmcs01.vmcs;
+
+		evmcs->hv_enlightenments_control.msr_bitmap = 1;
+	}
+
 	/* The MSR bitmap starts with all ones */
 	bitmap_fill(vmx->shadow_msr_intercept.read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
 	bitmap_fill(vmx->shadow_msr_intercept.write, MAX_POSSIBLE_PASSTHROUGH_MSRS);
-- 
2.31.1

[PATCH v4 6/8] KVM: VMX: Introduce vmx_msr_bitmap_l01_changed() helper

[Vitaly Kuznetsov]

In preparation to enabling 'Enlightened MSR Bitmap' feature for Hyper-V
guests move MSR bitmap update tracking to a dedicated helper.

Note: vmx_msr_bitmap_l01_changed() is called when MSR bitmap might be
updated. KVM doesn't check if the bit we're trying to set is already set
(or the bit it's trying to clear is already cleared). Such situations
should not be common and a few false positives should not be a problem.

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fc87b6bbd277..1e6bf2cd7be0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3677,6 +3677,17 @@ void free_vpid(int vpid)
 	spin_unlock(&vmx_vpid_lock);
 }
 
+static void vmx_msr_bitmap_l01_changed(struct vcpu_vmx *vmx)
+{
+	/*
+	 * When KVM is a nested hypervisor on top of Hyper-V and uses
+	 * 'Enlightened MSR Bitmap' feature L0 needs to know that MSR
+	 * bitmap has changed.
+	 */
+	if (static_branch_unlikely(&enable_evmcs))
+		evmcs_touch_msr_bitmap();
+}
+
 void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -3685,8 +3696,7 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
 
-	if (static_branch_unlikely(&enable_evmcs))
-		evmcs_touch_msr_bitmap();
+	vmx_msr_bitmap_l01_changed(vmx);
 
 	/*
 	 * Mark the desired intercept state in shadow bitmap, this is needed
@@ -3730,8 +3740,7 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
 
-	if (static_branch_unlikely(&enable_evmcs))
-		evmcs_touch_msr_bitmap();
+	vmx_msr_bitmap_l01_changed(vmx);
 
 	/*
 	 * Mark the desired intercept state in shadow bitmap, this is needed
-- 
2.31.1

[PATCH v4 7/8] KVM: nVMX: Track whether changes in L0 require MSR bitmap for L2 to be rebuilt

[Vitaly Kuznetsov]

Introduce a flag to keep track of whether MSR bitmap for L2 needs to be
rebuilt due to changes in MSR bitmap for L1 or switching to a different
L2. This information will be used for Enlightened MSR Bitmap feature for
Hyper-V guests.

Note, setting msr_bitmap_changed to 'true' from set_current_vmptr() is
not really needed for Enlightened MSR Bitmap as the feature can only
be used in conjunction with Enlightened VMCS but let's keep tracking
information complete, it's cheap and in the future similar PV feature can
easily be implemented for KVM on KVM too.

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 9 ++++++++-
 arch/x86/kvm/vmx/vmx.c    | 2 ++
 arch/x86/kvm/vmx/vmx.h    | 9 +++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 341c50816822..f02e846c944a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -664,6 +664,8 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 
 	kvm_vcpu_unmap(vcpu, &vmx->nested.msr_bitmap_map, false);
 
+	vmx->nested.force_msr_bitmap_recalc = false;
+
 	return true;
 }
 
@@ -2018,10 +2020,13 @@ static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
 	 * Clean fields data can't be used on VMLAUNCH and when we switch
 	 * between different L2 guests as KVM keeps a single VMCS12 per L1.
 	 */
-	if (from_launch || evmcs_gpa_changed)
+	if (from_launch || evmcs_gpa_changed) {
 		vmx->nested.hv_evmcs->hv_clean_fields &=
 			~HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
 
+		vmx->nested.force_msr_bitmap_recalc = true;
+	}
+
 	return EVMPTRLD_SUCCEEDED;
 }
 
@@ -5238,6 +5243,7 @@ static void set_current_vmptr(struct vcpu_vmx *vmx, gpa_t vmptr)
 		vmx->nested.need_vmcs12_to_shadow_sync = true;
 	}
 	vmx->nested.dirty_vmcs12 = true;
+	vmx->nested.force_msr_bitmap_recalc = true;
 }
 
 /* Emulate the VMPTRLD instruction */
@@ -6364,6 +6370,7 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 		goto error_guest_mode;
 
 	vmx->nested.dirty_vmcs12 = true;
+	vmx->nested.force_msr_bitmap_recalc = true;
 	ret = nested_vmx_enter_non_root_mode(vcpu, false);
 	if (ret)
 		goto error_guest_mode;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1e6bf2cd7be0..ec6635d1bcc4 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3686,6 +3686,8 @@ static void vmx_msr_bitmap_l01_changed(struct vcpu_vmx *vmx)
 	 */
 	if (static_branch_unlikely(&enable_evmcs))
 		evmcs_touch_msr_bitmap();
+
+	vmx->nested.force_msr_bitmap_recalc = true;
 }
 
 void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 86c093da0d63..8ad23f94917d 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -148,6 +148,15 @@ struct nested_vmx {
 	bool need_vmcs12_to_shadow_sync;
 	bool dirty_vmcs12;
 
+	/*
+	 * Indicates whether MSR bitmap for L2 needs to be rebuilt due to
+	 * changes in MSR bitmap for L1 or switching to a different L2. Note,
+	 * this flag can only be used reliably in conjunction with a paravirt L1
+	 * which informs L0 whether any changes to MSR bitmap for L2 were done
+	 * on its side.
+	 */
+	bool force_msr_bitmap_recalc;
+
 	/*
 	 * Indicates lazily loaded guest state has not yet been decached from
 	 * vmcs02.
-- 
2.31.1

[PATCH v4 8/8] KVM: nVMX: Implement Enlightened MSR Bitmap feature

[Vitaly Kuznetsov]

Updating MSR bitmap for L2 is not cheap and rearly needed. TLFS for Hyper-V
offers 'Enlightened MSR Bitmap' feature which allows L1 hypervisor to
inform L0 when it changes MSR bitmap, this eliminates the need to examine
L1's MSR bitmap for L2 every time when 'real' MSR bitmap for L2 gets
constructed.

Use 'vmx->nested.msr_bitmap_changed' flag to implement the feature.

Note, KVM already uses 'Enlightened MSR bitmap' feature when it runs as a
nested hypervisor on top of Hyper-V. The newly introduced feature is going
to be used by Hyper-V guests on KVM.

When the feature is enabled for Win10+WSL2, it shaves off around 700 CPU
cycles from a nested vmexit cost (tight cpuid loop test).

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/hyperv.c     |  2 ++
 arch/x86/kvm/vmx/nested.c | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 4f15c0165c05..948a34139e04 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2516,6 +2516,8 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 
 		case HYPERV_CPUID_NESTED_FEATURES:
 			ent->eax = evmcs_ver;
+			if (evmcs_ver)
+				ent->eax |= HV_X64_NESTED_MSR_BITMAP;
 
 			break;
 
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index f02e846c944a..5203810dab71 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -591,6 +591,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 	int msr;
 	unsigned long *msr_bitmap_l1;
 	unsigned long *msr_bitmap_l0 = vmx->nested.vmcs02.msr_bitmap;
+	struct hv_enlightened_vmcs *evmcs = vmx->nested.hv_evmcs;
 	struct kvm_host_map *map = &vmx->nested.msr_bitmap_map;
 
 	/* Nothing to do if the MSR bitmap is not in use.  */
@@ -598,6 +599,19 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 	    !nested_cpu_has(vmcs12, CPU_BASED_USE_MSR_BITMAPS))
 		return false;
 
+	/*
+	 * MSR bitmap update can be skipped when:
+	 * - MSR bitmap for L1 hasn't changed.
+	 * - Nested hypervisor (L1) is attempting to launch the same L2 as
+	 *   before.
+	 * - Nested hypervisor (L1) has enabled 'Enlightened MSR Bitmap' feature
+	 *   and tells KVM (L0) there were no changes in MSR bitmap for L2.
+	 */
+	if (!vmx->nested.force_msr_bitmap_recalc && evmcs &&
+	    evmcs->hv_enlightenments_control.msr_bitmap &&
+	    evmcs->hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP)
+		return true;
+
 	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->msr_bitmap), map))
 		return false;
 
-- 
2.31.1

Re: [PATCH v4 0/8] KVM: nVMX: Enlightened MSR Bitmap feature for Hyper-V on KVM (+ KVM: x86: MSR filtering and related fixes)

[Sean Christopherson]

On Tue, Nov 09, 2021, Vitaly Kuznetsov wrote:
> This series combines "Enlightened MSR Bitmap feature for Hyper-V on KVM v4"
> and Sean's "KVM: x86: MSR filtering and related fixes v4" 
> (https://lore.kernel.org/kvm/20211109013047.2041518-1-seanjc@google.com/)
> series as they're code dependent.

Series as a whole looks good, thanks for doing the dirty work!