[PATCH v5 01/26] KVM: nSVM: Avoid clearing VMCB_LBR in vmcb12

[PATCH v5 01/26] KVM: nSVM: Avoid clearing VMCB_LBR in vmcb12

[Yosry Ahmed]

svm_copy_lbrs() always marks VMCB_LBR dirty in the destination VMCB.
However, nested_svm_vmexit() uses it to copy LBRs to vmcb12, and
clearing clean bits in vmcb12 is not architecturally defined.

Move vmcb_mark_dirty() to callers and drop it for vmcb12.

This also facilitates incoming refactoring that does not pass the entire
VMCB to svm_copy_lbrs().

Fixes: d20c796ca370 ("KVM: x86: nSVM: implement nested LBR virtualization")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 7 +++++--
 arch/x86/kvm/svm/svm.c    | 2 --
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index de90b104a0dd..a31f3be1e16e 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -714,6 +714,7 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 	} else {
 		svm_copy_lbrs(vmcb02, vmcb01);
 	}
+	vmcb_mark_dirty(vmcb02, VMCB_LBR);
 	svm_update_lbrv(&svm->vcpu);
 }
 
@@ -1232,10 +1233,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 		kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
 
 	if (unlikely(guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
-		     (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK)))
+		     (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
 		svm_copy_lbrs(vmcb12, vmcb02);
-	else
+	} else {
 		svm_copy_lbrs(vmcb01, vmcb02);
+		vmcb_mark_dirty(vmcb01, VMCB_LBR);
+	}
 
 	svm_update_lbrv(vcpu);
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5f0136dbdde6..98cbd7c7beed 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -848,8 +848,6 @@ void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
 	to_vmcb->save.br_to		= from_vmcb->save.br_to;
 	to_vmcb->save.last_excp_from	= from_vmcb->save.last_excp_from;
 	to_vmcb->save.last_excp_to	= from_vmcb->save.last_excp_to;
-
-	vmcb_mark_dirty(to_vmcb, VMCB_LBR);
 }
 
 static void __svm_enable_lbrv(struct kvm_vcpu *vcpu)
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 02/26] KVM: SVM: Switch svm_copy_lbrs() to a macro

[Yosry Ahmed]

In preparation for using svm_copy_lbrs() with 'struct vmcb_save_area'
without a containing 'struct vmcb', and later even 'struct
vmcb_save_area_cached', make it a macro.

Macros are generally not preferred compared to functions, mainly due to
type-safety. However, in this case it seems like having a simple macro
copying a few fields is better than copy-pasting the same 5 lines of
code in different places.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c |  8 ++++----
 arch/x86/kvm/svm/svm.c    |  9 ---------
 arch/x86/kvm/svm/svm.h    | 10 +++++++++-
 3 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index a31f3be1e16e..f7d5db0af69a 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -709,10 +709,10 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 		 * Reserved bits of DEBUGCTL are ignored.  Be consistent with
 		 * svm_set_msr's definition of reserved bits.
 		 */
-		svm_copy_lbrs(vmcb02, vmcb12);
+		svm_copy_lbrs(&vmcb02->save, &vmcb12->save);
 		vmcb02->save.dbgctl &= ~DEBUGCTL_RESERVED_BITS;
 	} else {
-		svm_copy_lbrs(vmcb02, vmcb01);
+		svm_copy_lbrs(&vmcb02->save, &vmcb01->save);
 	}
 	vmcb_mark_dirty(vmcb02, VMCB_LBR);
 	svm_update_lbrv(&svm->vcpu);
@@ -1234,9 +1234,9 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	if (unlikely(guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
 		     (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
-		svm_copy_lbrs(vmcb12, vmcb02);
+		svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
 	} else {
-		svm_copy_lbrs(vmcb01, vmcb02);
+		svm_copy_lbrs(&vmcb01->save, &vmcb02->save);
 		vmcb_mark_dirty(vmcb01, VMCB_LBR);
 	}
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 98cbd7c7beed..798f2c84d80b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -841,15 +841,6 @@ static void svm_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 	 */
 }
 
-void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
-{
-	to_vmcb->save.dbgctl		= from_vmcb->save.dbgctl;
-	to_vmcb->save.br_from		= from_vmcb->save.br_from;
-	to_vmcb->save.br_to		= from_vmcb->save.br_to;
-	to_vmcb->save.last_excp_from	= from_vmcb->save.last_excp_from;
-	to_vmcb->save.last_excp_to	= from_vmcb->save.last_excp_to;
-}
-
 static void __svm_enable_lbrv(struct kvm_vcpu *vcpu)
 {
 	to_svm(vcpu)->vmcb->control.virt_ext |= LBR_CTL_ENABLE_MASK;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ebd7b36b1ceb..44d767cd1d25 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -713,8 +713,16 @@ static inline void *svm_vcpu_alloc_msrpm(void)
 	return svm_alloc_permissions_map(MSRPM_SIZE, GFP_KERNEL_ACCOUNT);
 }
 
+#define svm_copy_lbrs(to, from)					\
+do {								\
+	(to)->dbgctl		= (from)->dbgctl;		\
+	(to)->br_from		= (from)->br_from;		\
+	(to)->br_to		= (from)->br_to;		\
+	(to)->last_excp_from	= (from)->last_excp_from;	\
+	(to)->last_excp_to	= (from)->last_excp_to;		\
+} while (0)
+
 void svm_vcpu_free_msrpm(void *msrpm);
-void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb);
 void svm_enable_lbrv(struct kvm_vcpu *vcpu);
 void svm_update_lbrv(struct kvm_vcpu *vcpu);
 
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 03/26] KVM: SVM: Add missing save/restore handling of LBR MSRs

[Yosry Ahmed]

MSR_IA32_DEBUGCTLMSR and LBR MSRs are currently not enumerated by
KVM_GET_MSR_INDEX_LIST, and LBR MSRs cannot be set with KVM_SET_MSRS. So
save/restore is completely broken.

Fix it by adding the MSRs to msrs_to_save_base, and allowing writes to
LBR MSRs from userspace only (as they are read-only MSRs). Additionally,
to correctly restore L1's LBRs while L2 is running, make sure the LBRs
are copied from the captured VMCB01 save area in svm_copy_vmrun_state().

Fixes: 24e09cbf480a ("KVM: SVM: enable LBR virtualization")
Cc: stable@vger.kernel.org
Reported-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c |  3 +++
 arch/x86/kvm/svm/svm.c    | 20 ++++++++++++++++++++
 arch/x86/kvm/x86.c        |  3 +++
 3 files changed, 26 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index f7d5db0af69a..52d853684592 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1100,6 +1100,9 @@ void svm_copy_vmrun_state(struct vmcb_save_area *to_save,
 		to_save->isst_addr = from_save->isst_addr;
 		to_save->ssp = from_save->ssp;
 	}
+
+	if (lbrv)
+		svm_copy_lbrs(to_save, from_save);
 }
 
 void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 798f2c84d80b..d93414db6559 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3071,6 +3071,26 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		vmcb_mark_dirty(svm->vmcb, VMCB_LBR);
 		svm_update_lbrv(vcpu);
 		break;
+	case MSR_IA32_LASTBRANCHFROMIP:
+		if (!msr->host_initiated)
+			return 1;
+		svm->vmcb->save.br_from = data;
+		break;
+	case MSR_IA32_LASTBRANCHTOIP:
+		if (!msr->host_initiated)
+			return 1;
+		svm->vmcb->save.br_to = data;
+		break;
+	case MSR_IA32_LASTINTFROMIP:
+		if (!msr->host_initiated)
+			return 1;
+		svm->vmcb->save.last_excp_from = data;
+		break;
+	case MSR_IA32_LASTINTTOIP:
+		if (!msr->host_initiated)
+			return 1;
+		svm->vmcb->save.last_excp_to = data;
+		break;
 	case MSR_VM_HSAVE_PA:
 		/*
 		 * Old kernels did not validate the value written to
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index db3f393192d9..416899b5dbe4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -351,6 +351,9 @@ static const u32 msrs_to_save_base[] = {
 	MSR_IA32_U_CET, MSR_IA32_S_CET,
 	MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, MSR_IA32_PL2_SSP,
 	MSR_IA32_PL3_SSP, MSR_IA32_INT_SSP_TAB,
+	MSR_IA32_DEBUGCTLMSR,
+	MSR_IA32_LASTBRANCHFROMIP, MSR_IA32_LASTBRANCHTOIP,
+	MSR_IA32_LASTINTFROMIP, MSR_IA32_LASTINTTOIP,
 };
 
 static const u32 msrs_to_save_pmu[] = {
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 05/26] KVM: nSVM: Always inject a #GP if mapping VMCB12 fails on nested VMRUN

[Yosry Ahmed]

nested_svm_vmrun() currently only injects a #GP if kvm_vcpu_map() fails
with -EINVAL. But it could also fail with -EFAULT if creating a host
mapping failed. Inject a #GP in all cases, no reason to treat failure
modes differently.

Fixes: 8c5fbf1a7231 ("KVM/nSVM: Use the new mapping API for mapping guest memory")
CC: stable@vger.kernel.org
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 52d853684592..fab0d3d5baa2 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1011,12 +1011,9 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 	}
 
 	vmcb12_gpa = svm->vmcb->save.rax;
-	ret = kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map);
-	if (ret == -EINVAL) {
+	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
 		kvm_inject_gp(vcpu, 0);
 		return 1;
-	} else if (ret) {
-		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	ret = kvm_skip_emulated_instruction(vcpu);
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 06/26] KVM: nSVM: Triple fault if mapping VMCB12 fails on nested #VMEXIT

[Yosry Ahmed]

KVM currently injects a #GP and hopes for the best if mapping VMCB12
fails on nested #VMEXIT, and only if the failure mode is -EINVAL.
Mapping the VMCB12 could also fail if creating host mappings fails.

After the #GP is injected, nested_svm_vmexit() bails early, without
cleaning up (e.g. KVM_REQ_GET_NESTED_STATE_PAGES is set, is_guest_mode()
is true, etc). Move mapping VMCB12 a bit later, after leaving guest mode
and clearing KVM_REQ_GET_NESTED_STATE_PAGES, right before the VMCB12 is
actually used.

Instead of optionally injecting a #GP, triple fault the guest if mapping
VMCB12 fails since KVM cannot make a sane recovery. The APM states that
a #VMEXIT will triple fault if host state is illegal or an exception
occurs while loading host state, so the behavior is not entirely made
up.

Also update the WARN_ON() in svm_get_nested_state_pages() to
WARN_ON_ONCE() to avoid future user-triggeable bugs spamming kernel logs
and potentially causing issues.

Fixes: cf74a78b229d ("KVM: SVM: Add VMEXIT handler and intercepts")
CC: stable@vger.kernel.org
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index fab0d3d5baa2..830341b0e1f8 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1121,24 +1121,14 @@ void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
 int nested_svm_vmexit(struct vcpu_svm *svm)
 {
 	struct kvm_vcpu *vcpu = &svm->vcpu;
+	gpa_t vmcb12_gpa = svm->nested.vmcb12_gpa;
 	struct vmcb *vmcb01 = svm->vmcb01.ptr;
 	struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
 	struct vmcb *vmcb12;
 	struct kvm_host_map map;
-	int rc;
-
-	rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map);
-	if (rc) {
-		if (rc == -EINVAL)
-			kvm_inject_gp(vcpu, 0);
-		return 1;
-	}
-
-	vmcb12 = map.hva;
 
 	/* Exit Guest-Mode */
 	leave_guest_mode(vcpu);
-	svm->nested.vmcb12_gpa = 0;
 	WARN_ON_ONCE(svm->nested.nested_run_pending);
 
 	kvm_clear_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
@@ -1146,8 +1136,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	/* in case we halted in L2 */
 	kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
 
+	svm->nested.vmcb12_gpa = 0;
+
+	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
+		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+		return 1;
+	}
+
 	/* Give the current vmcb to the guest */
 
+	vmcb12 = map.hva;
 	vmcb12->save.es     = vmcb02->save.es;
 	vmcb12->save.cs     = vmcb02->save.cs;
 	vmcb12->save.ss     = vmcb02->save.ss;
@@ -1304,8 +1302,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	nested_svm_uninit_mmu_context(vcpu);
 
-	rc = nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true);
-	if (rc)
+	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true))
 		return 1;
 
 	/*
@@ -1936,7 +1933,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 {
-	if (WARN_ON(!is_guest_mode(vcpu)))
+	if (WARN_ON_ONCE(!is_guest_mode(vcpu)))
 		return true;
 
 	if (!vcpu->arch.pdptrs_from_userspace &&
-- 
2.53.0.rc2.204.g2597b5adb4-goog

Re: [PATCH v5 06/26] KVM: nSVM: Triple fault if mapping VMCB12 fails on nested #VMEXIT

[Sean Christopherson]

On Fri, Feb 06, 2026, Yosry Ahmed wrote:
> KVM currently injects a #GP and hopes for the best if mapping VMCB12
> fails on nested #VMEXIT, and only if the failure mode is -EINVAL.
> Mapping the VMCB12 could also fail if creating host mappings fails.
> 
> After the #GP is injected, nested_svm_vmexit() bails early, without
> cleaning up (e.g. KVM_REQ_GET_NESTED_STATE_PAGES is set, is_guest_mode()
> is true, etc). Move mapping VMCB12 a bit later, after leaving guest mode
> and clearing KVM_REQ_GET_NESTED_STATE_PAGES, right before the VMCB12 is
> actually used.
> 
> Instead of optionally injecting a #GP, triple fault the guest if mapping
> VMCB12 fails since KVM cannot make a sane recovery. The APM states that
> a #VMEXIT will triple fault if host state is illegal or an exception
> occurs while loading host state, so the behavior is not entirely made
> up.
> 
> Also update the WARN_ON() in svm_get_nested_state_pages() to
> WARN_ON_ONCE() to avoid future user-triggeable bugs spamming kernel logs
> and potentially causing issues.
> 
> Fixes: cf74a78b229d ("KVM: SVM: Add VMEXIT handler and intercepts")
> CC: stable@vger.kernel.org
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
>  arch/x86/kvm/svm/nested.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index fab0d3d5baa2..830341b0e1f8 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1121,24 +1121,14 @@ void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
>  int nested_svm_vmexit(struct vcpu_svm *svm)
>  {
>  	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	gpa_t vmcb12_gpa = svm->nested.vmcb12_gpa;
>  	struct vmcb *vmcb01 = svm->vmcb01.ptr;
>  	struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
>  	struct vmcb *vmcb12;
>  	struct kvm_host_map map;
> -	int rc;
> -
> -	rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map);
> -	if (rc) {
> -		if (rc == -EINVAL)
> -			kvm_inject_gp(vcpu, 0);
> -		return 1;
> -	}
> -
> -	vmcb12 = map.hva;
>  
>  	/* Exit Guest-Mode */
>  	leave_guest_mode(vcpu);
> -	svm->nested.vmcb12_gpa = 0;
>  	WARN_ON_ONCE(svm->nested.nested_run_pending);
>  
>  	kvm_clear_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
> @@ -1146,8 +1136,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>  	/* in case we halted in L2 */
>  	kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
>  
> +	svm->nested.vmcb12_gpa = 0;
> +
> +	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
> +		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> +		return 1;

Returning early isn't entirely correct.  In fact, I think it's worse than the
current behavior in many aspects.

By doing leave_guest_mode() and not switching back to vmcb01 and not putting
vcpu->arch.mmu back to root_mmu, the vCPU will be in L1 but with vmcb02 and L2's
MMU active.

The idea I can come up with is to isolate the vmcb12 writes (which is suprisingly
straightforward), and then simply skip the vmcb12 updates.  E.g.

---
 arch/x86/kvm/svm/nested.c | 95 ++++++++++++++++++++++-----------------
 1 file changed, 54 insertions(+), 41 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index fab0d3d5baa2..e8c163d95364 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -639,6 +639,12 @@ void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm)
 	svm->nested.vmcb02.ptr->save.g_pat = svm->vmcb01.ptr->save.g_pat;
 }
 
+static bool nested_vmcb12_has_lbrv(struct kvm_vcpu *vcpu)
+{
+	return guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
+	       to_svm(vcpu)->nested.ctl.virt_ext;
+}
+
 static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12)
 {
 	bool new_vmcb12 = false;
@@ -703,8 +709,7 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 		vmcb_mark_dirty(vmcb02, VMCB_DR);
 	}
 
-	if (unlikely(guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
-		     (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
+	if (nested_vmcb12_has_lbrv(vcpu)) {
 		/*
 		 * Reserved bits of DEBUGCTL are ignored.  Be consistent with
 		 * svm_set_msr's definition of reserved bits.
@@ -1118,35 +1123,14 @@ void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
 	to_vmcb->save.sysenter_eip = from_vmcb->save.sysenter_eip;
 }
 
-int nested_svm_vmexit(struct vcpu_svm *svm)
+static void nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu,
+					    struct vmcb *vmcb12,
+					    struct vmcb *vmcb02)
 {
-	struct kvm_vcpu *vcpu = &svm->vcpu;
-	struct vmcb *vmcb01 = svm->vmcb01.ptr;
-	struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
-	struct vmcb *vmcb12;
-	struct kvm_host_map map;
-	int rc;
+	struct vcpu_svm *svm = to_svm(vcpu);
 
-	rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map);
-	if (rc) {
-		if (rc == -EINVAL)
-			kvm_inject_gp(vcpu, 0);
-		return 1;
-	}
-
-	vmcb12 = map.hva;
-
-	/* Exit Guest-Mode */
-	leave_guest_mode(vcpu);
-	svm->nested.vmcb12_gpa = 0;
-	WARN_ON_ONCE(svm->nested.nested_run_pending);
-
-	kvm_clear_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
-
-	/* in case we halted in L2 */
-	kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
-
-	/* Give the current vmcb to the guest */
+	if (!vmcb12)
+		return;
 
 	vmcb12->save.es     = vmcb02->save.es;
 	vmcb12->save.cs     = vmcb02->save.cs;
@@ -1184,14 +1168,53 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
 		vmcb12->control.next_rip  = vmcb02->control.next_rip;
 
+	if (nested_vmcb12_has_lbrv(vcpu))
+		svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
+
 	vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
 	vmcb12->control.event_inj         = svm->nested.ctl.event_inj;
 	vmcb12->control.event_inj_err     = svm->nested.ctl.event_inj_err;
 
+	trace_kvm_nested_vmexit_inject(vmcb12->control.exit_code,
+				       vmcb12->control.exit_info_1,
+				       vmcb12->control.exit_info_2,
+				       vmcb12->control.exit_int_info,
+				       vmcb12->control.exit_int_info_err,
+				       KVM_ISA_SVM);
+}
+
+int nested_svm_vmexit(struct vcpu_svm *svm)
+{
+	struct kvm_vcpu *vcpu = &svm->vcpu;
+	struct vmcb *vmcb01 = svm->vmcb01.ptr;
+	struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
+	struct vmcb *vmcb12;
+	struct kvm_host_map map;
+	int rc;
+
+	if (!kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map)) {
+		vmcb12 = map.hva;
+	} else {
+		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+		vmcb12 = NULL;
+	}
+
+	/* Exit Guest-Mode */
+	leave_guest_mode(vcpu);
+	svm->nested.vmcb12_gpa = 0;
+	WARN_ON_ONCE(svm->nested.nested_run_pending);
+
+	kvm_clear_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
+
+	/* in case we halted in L2 */
+	kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
+
+	/* Give the current vmcb to the guest */
+	nested_svm_vmexit_update_vmcb12(vcpu, vmcb12, vmcb02);
+
 	if (!kvm_pause_in_guest(vcpu->kvm)) {
 		vmcb01->control.pause_filter_count = vmcb02->control.pause_filter_count;
 		vmcb_mark_dirty(vmcb01, VMCB_INTERCEPTS);
-
 	}
 
 	/*
@@ -1232,10 +1255,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	if (!nested_exit_on_intr(svm))
 		kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
 
-	if (unlikely(guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
-		     (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
-		svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
-	} else {
+	if (!nested_vmcb12_has_lbrv(vcpu)) {
 		svm_copy_lbrs(&vmcb01->save, &vmcb02->save);
 		vmcb_mark_dirty(vmcb01, VMCB_LBR);
 	}
@@ -1291,13 +1311,6 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	svm->vcpu.arch.dr7 = DR7_FIXED_1;
 	kvm_update_dr7(&svm->vcpu);
 
-	trace_kvm_nested_vmexit_inject(vmcb12->control.exit_code,
-				       vmcb12->control.exit_info_1,
-				       vmcb12->control.exit_info_2,
-				       vmcb12->control.exit_int_info,
-				       vmcb12->control.exit_int_info_err,
-				       KVM_ISA_SVM);
-
 	kvm_vcpu_unmap(vcpu, &map);
 
 	nested_svm_transition_tlb_flush(vcpu);

base-commit: 2125912d022f4740238a950469da505783945be6
--

Re: [PATCH v5 06/26] KVM: nSVM: Triple fault if mapping VMCB12 fails on nested #VMEXIT

[Yosry Ahmed]

> > @@ -1146,8 +1136,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> >       /* in case we halted in L2 */
> >       kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
> >
> > +     svm->nested.vmcb12_gpa = 0;
> > +
> > +     if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
> > +             kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> > +             return 1;
>
> Returning early isn't entirely correct.  In fact, I think it's worse than the
> current behavior in many aspects.
>
> By doing leave_guest_mode() and not switching back to vmcb01 and not putting
> vcpu->arch.mmu back to root_mmu, the vCPU will be in L1 but with vmcb02 and L2's
> MMU active.

Hmm yeah, the same problem also exists in
nested_svm_vmrun_error_vmexit() after "KVM: nSVM: Restrict mapping
VMCB12 on nested VMRUN". In that path, we only need to map vmcb12 to
zero event_inj in __nested_svm_vmexit(). We can probably move them to
the callers (nested_svm_vmrun_error_vmexit() and nested_svm_vmexit())
to make it easier to skip if mapping fails.

>
> The idea I can come up with is to isolate the vmcb12 writes (which is suprisingly
> straightforward), and then simply skip the vmcb12 updates.  E.g.
>
> ---
[..]
> @@ -1184,14 +1168,53 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>         if (guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
>                 vmcb12->control.next_rip  = vmcb02->control.next_rip;
>
> +       if (nested_vmcb12_has_lbrv(vcpu))
> +               svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
> +
>         vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
>         vmcb12->control.event_inj         = svm->nested.ctl.event_inj;
>         vmcb12->control.event_inj_err     = svm->nested.ctl.event_inj_err;
>
> +       trace_kvm_nested_vmexit_inject(vmcb12->control.exit_code,
> +                                      vmcb12->control.exit_info_1,
> +                                      vmcb12->control.exit_info_2,
> +                                      vmcb12->control.exit_int_info,
> +                                      vmcb12->control.exit_int_info_err,
> +                                      KVM_ISA_SVM);
> +}
> +
> +int nested_svm_vmexit(struct vcpu_svm *svm)
> +{
> +       struct kvm_vcpu *vcpu = &svm->vcpu;
> +       struct vmcb *vmcb01 = svm->vmcb01.ptr;
> +       struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
> +       struct vmcb *vmcb12;
> +       struct kvm_host_map map;
> +       int rc;
> +
> +       if (!kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map)) {
> +               vmcb12 = map.hva;

Maybe also kvm_vcpu_map() mapping call to
nested_svm_vmexit_update_vmcb12() and inject a tripe fault if it
fails? Probably plays nicer with "KVM: nSVM: Restrict mapping VMCB12
on nested VMRUN".

Otherwise it looks good to me.

Should I send a new version to add all the changes?

Re: [PATCH v5 06/26] KVM: nSVM: Triple fault if mapping VMCB12 fails on nested #VMEXIT

[Sean Christopherson]

On Mon, Feb 23, 2026, Yosry Ahmed wrote:
> > > @@ -1146,8 +1136,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> > >       /* in case we halted in L2 */
> > >       kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
> > >
> > > +     svm->nested.vmcb12_gpa = 0;
> > > +
> > > +     if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
> > > +             kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> > > +             return 1;
> >
> > Returning early isn't entirely correct.  In fact, I think it's worse than the
> > current behavior in many aspects.
> >
> > By doing leave_guest_mode() and not switching back to vmcb01 and not putting
> > vcpu->arch.mmu back to root_mmu, the vCPU will be in L1 but with vmcb02 and L2's
> > MMU active.
> 
> Hmm yeah, the same problem also exists in
> nested_svm_vmrun_error_vmexit() after "KVM: nSVM: Restrict mapping
> VMCB12 on nested VMRUN". In that path, we only need to map vmcb12 to
> zero event_inj in __nested_svm_vmexit(). We can probably move them to
> the callers (nested_svm_vmrun_error_vmexit() and nested_svm_vmexit())
> to make it easier to skip if mapping fails.

Agreed, I don't see a better option.

> > The idea I can come up with is to isolate the vmcb12 writes (which is suprisingly
> > straightforward), and then simply skip the vmcb12 updates.  E.g.
> >
> > ---
> [..]
> > @@ -1184,14 +1168,53 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> >         if (guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
> >                 vmcb12->control.next_rip  = vmcb02->control.next_rip;
> >
> > +       if (nested_vmcb12_has_lbrv(vcpu))
> > +               svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
> > +
> >         vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
> >         vmcb12->control.event_inj         = svm->nested.ctl.event_inj;
> >         vmcb12->control.event_inj_err     = svm->nested.ctl.event_inj_err;
> >
> > +       trace_kvm_nested_vmexit_inject(vmcb12->control.exit_code,
> > +                                      vmcb12->control.exit_info_1,
> > +                                      vmcb12->control.exit_info_2,
> > +                                      vmcb12->control.exit_int_info,
> > +                                      vmcb12->control.exit_int_info_err,
> > +                                      KVM_ISA_SVM);
> > +}
> > +
> > +int nested_svm_vmexit(struct vcpu_svm *svm)
> > +{
> > +       struct kvm_vcpu *vcpu = &svm->vcpu;
> > +       struct vmcb *vmcb01 = svm->vmcb01.ptr;
> > +       struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
> > +       struct vmcb *vmcb12;
> > +       struct kvm_host_map map;
> > +       int rc;
> > +
> > +       if (!kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map)) {
> > +               vmcb12 = map.hva;
> 
> Maybe also kvm_vcpu_map() mapping call to
> nested_svm_vmexit_update_vmcb12() and inject a tripe fault if it
> fails? Probably plays nicer with "KVM: nSVM: Restrict mapping VMCB12
> on nested VMRUN".

Oh, yeah, good call!  That would be way cleaner (I initially didn't move all
vmcb12 reference, but that's a *really* good argument for doing so).

> Otherwise it looks good to me.
> 
> Should I send a new version to add all the changes?

Yes please.  Thanks!

[PATCH v5 07/26] KVM: nSVM: Triple fault if restore host CR3 fails on nested #VMEXIT

[Yosry Ahmed]

If loading L1's CR3 fails on a nested #VMEXIT, nested_svm_vmexit()
returns an error code that is ignored by most callers, and continues to
run L1 with corrupted state. A sane recovery is not possible in this
case, and HW behavior is to cause a shutdown. Inject a triple fault
instead.

From the APM:
	Upon #VMEXIT, the processor performs the following actions in
	order to return to the host execution context:

	...
	if (illegal host state loaded, or exception while loading
	    host state)
		shutdown
	else
		execute first host instruction following the VMRUN

Remove the return value of nested_svm_vmexit(), which is mostly
unchecked anyway.

Fixes: d82aaef9c88a ("KVM: nSVM: use nested_svm_load_cr3() on guest->host switch")
CC: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 12 ++++++------
 arch/x86/kvm/svm/svm.c    | 11 ++---------
 arch/x86/kvm/svm/svm.h    |  6 +++---
 3 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 830341b0e1f8..33e6e1e77aac 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1118,7 +1118,7 @@ void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
 	to_vmcb->save.sysenter_eip = from_vmcb->save.sysenter_eip;
 }
 
-int nested_svm_vmexit(struct vcpu_svm *svm)
+void nested_svm_vmexit(struct vcpu_svm *svm)
 {
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 	gpa_t vmcb12_gpa = svm->nested.vmcb12_gpa;
@@ -1140,7 +1140,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
 		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
-		return 1;
+		return;
 	}
 
 	/* Give the current vmcb to the guest */
@@ -1302,8 +1302,10 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	nested_svm_uninit_mmu_context(vcpu);
 
-	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true))
-		return 1;
+	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true)) {
+		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+		return;
+	}
 
 	/*
 	 * Drop what we picked up for L2 via svm_complete_interrupts() so it
@@ -1328,8 +1330,6 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	 */
 	if (kvm_apicv_activated(vcpu->kvm))
 		__kvm_vcpu_update_apicv(vcpu);
-
-	return 0;
 }
 
 static void nested_svm_triple_fault(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d93414db6559..a534c08fbe61 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2234,13 +2234,9 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 		[SVM_INSTR_VMSAVE] = vmsave_interception,
 	};
 	struct vcpu_svm *svm = to_svm(vcpu);
-	int ret;
 
 	if (is_guest_mode(vcpu)) {
-		/* Returns '1' or -errno on failure, '0' on success. */
-		ret = nested_svm_simple_vmexit(svm, guest_mode_exit_codes[opcode]);
-		if (ret)
-			return ret;
+		nested_svm_simple_vmexit(svm, guest_mode_exit_codes[opcode]);
 		return 1;
 	}
 	return svm_instr_handlers[opcode](vcpu);
@@ -4792,7 +4788,6 @@ static int svm_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	struct kvm_host_map map_save;
-	int ret;
 
 	if (!is_guest_mode(vcpu))
 		return 0;
@@ -4812,9 +4807,7 @@ static int svm_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram)
 	svm->vmcb->save.rsp = vcpu->arch.regs[VCPU_REGS_RSP];
 	svm->vmcb->save.rip = vcpu->arch.regs[VCPU_REGS_RIP];
 
-	ret = nested_svm_simple_vmexit(svm, SVM_EXIT_SW);
-	if (ret)
-		return ret;
+	nested_svm_simple_vmexit(svm, SVM_EXIT_SW);
 
 	/*
 	 * KVM uses VMCB01 to store L1 host state while L2 runs but
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 44d767cd1d25..7629cb37c930 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -793,14 +793,14 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu);
 void svm_copy_vmrun_state(struct vmcb_save_area *to_save,
 			  struct vmcb_save_area *from_save);
 void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb);
-int nested_svm_vmexit(struct vcpu_svm *svm);
+void nested_svm_vmexit(struct vcpu_svm *svm);
 
-static inline int nested_svm_simple_vmexit(struct vcpu_svm *svm, u32 exit_code)
+static inline void nested_svm_simple_vmexit(struct vcpu_svm *svm, u32 exit_code)
 {
 	svm->vmcb->control.exit_code	= exit_code;
 	svm->vmcb->control.exit_info_1	= 0;
 	svm->vmcb->control.exit_info_2	= 0;
-	return nested_svm_vmexit(svm);
+	nested_svm_vmexit(svm);
 }
 
 int nested_svm_exit_handled(struct vcpu_svm *svm);
-- 
2.53.0.rc2.204.g2597b5adb4-goog

Re: [PATCH v5 07/26] KVM: nSVM: Triple fault if restore host CR3 fails on nested #VMEXIT

[Sean Christopherson]

On Fri, Feb 06, 2026, Yosry Ahmed wrote:
> @@ -1140,7 +1140,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>  
>  	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
>  		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> -		return 1;
> +		return;
>  	}

And then here I think we can do the same thing, e.g.

	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true))
		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);

[PATCH v5 08/26] KVM: nSVM: Drop nested_vmcb_check_{save/control}() wrappers

[Yosry Ahmed]

The wrappers provide little value and make it harder to see what KVM is
checking in the normal flow. Drop them.

Opportunistically fixup comments referring to the functions, adding '()'
to make it clear it's a reference to a function.

No functional change intended.

Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 36 ++++++++++--------------------------
 1 file changed, 10 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 33e6e1e77aac..29069fc5e8cb 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -339,8 +339,8 @@ static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa, u32 size)
 	    kvm_vcpu_is_legal_gpa(vcpu, addr + size - 1);
 }
 
-static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
-					 struct vmcb_ctrl_area_cached *control)
+static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
+				       struct vmcb_ctrl_area_cached *control)
 {
 	if (CC(!vmcb12_is_intercept(control, INTERCEPT_VMRUN)))
 		return false;
@@ -367,8 +367,8 @@ static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 }
 
 /* Common checks that apply to both L1 and L2 state.  */
-static bool __nested_vmcb_check_save(struct kvm_vcpu *vcpu,
-				     struct vmcb_save_area_cached *save)
+static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
+				   struct vmcb_save_area_cached *save)
 {
 	if (CC(!(save->efer & EFER_SVME)))
 		return false;
@@ -402,22 +402,6 @@ static bool __nested_vmcb_check_save(struct kvm_vcpu *vcpu,
 	return true;
 }
 
-static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_svm *svm = to_svm(vcpu);
-	struct vmcb_save_area_cached *save = &svm->nested.save;
-
-	return __nested_vmcb_check_save(vcpu, save);
-}
-
-static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_svm *svm = to_svm(vcpu);
-	struct vmcb_ctrl_area_cached *ctl = &svm->nested.ctl;
-
-	return __nested_vmcb_check_controls(vcpu, ctl);
-}
-
 /*
  * If a feature is not advertised to L1, clear the corresponding vmcb12
  * intercept.
@@ -469,7 +453,7 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	to->pause_filter_count  = from->pause_filter_count;
 	to->pause_filter_thresh = from->pause_filter_thresh;
 
-	/* Copy asid here because nested_vmcb_check_controls will check it.  */
+	/* Copy asid here because nested_vmcb_check_controls() will check it */
 	to->asid           = from->asid;
 	to->msrpm_base_pa &= ~0x0fffULL;
 	to->iopm_base_pa  &= ~0x0fffULL;
@@ -1026,8 +1010,8 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 	nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
 	nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
 
-	if (!nested_vmcb_check_save(vcpu) ||
-	    !nested_vmcb_check_controls(vcpu)) {
+	if (!nested_vmcb_check_save(vcpu, &svm->nested.save) ||
+	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {
 		vmcb12->control.exit_code    = SVM_EXIT_ERR;
 		vmcb12->control.exit_info_1  = 0;
 		vmcb12->control.exit_info_2  = 0;
@@ -1861,12 +1845,12 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 	ret = -EINVAL;
 	__nested_copy_vmcb_control_to_cache(vcpu, &ctl_cached, ctl);
-	if (!__nested_vmcb_check_controls(vcpu, &ctl_cached))
+	if (!nested_vmcb_check_controls(vcpu, &ctl_cached))
 		goto out_free;
 
 	/*
 	 * Processor state contains L2 state.  Check that it is
-	 * valid for guest mode (see nested_vmcb_check_save).
+	 * valid for guest mode (see nested_vmcb_check_save()).
 	 */
 	cr0 = kvm_read_cr0(vcpu);
         if (((cr0 & X86_CR0_CD) == 0) && (cr0 & X86_CR0_NW))
@@ -1880,7 +1864,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	if (!(save->cr0 & X86_CR0_PG) ||
 	    !(save->cr0 & X86_CR0_PE) ||
 	    (save->rflags & X86_EFLAGS_VM) ||
-	    !__nested_vmcb_check_save(vcpu, &save_cached))
+	    !nested_vmcb_check_save(vcpu, &save_cached))
 		goto out_free;
 
 
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 09/26] KVM: nSVM: Call enter_guest_mode() before switching to VMCB02

[Yosry Ahmed]

In preparation for moving more changes that rely on is_guest_mode()
before switching to VMCB02, move entering guest mode a bit earlier.

Nothing between the new callsite(s) and the old ones rely on
is_guest_mode(), so this should be safe.

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 29069fc5e8cb..607d99172e2b 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -741,9 +741,6 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
 
 	nested_svm_transition_tlb_flush(vcpu);
 
-	/* Enter Guest-Mode */
-	enter_guest_mode(vcpu);
-
 	/*
 	 * Filled at exit: exit_code, exit_info_1, exit_info_2, exit_int_info,
 	 * exit_int_info_err, next_rip, insn_len, insn_bytes.
@@ -944,6 +941,8 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 
 	WARN_ON(svm->vmcb == svm->nested.vmcb02.ptr);
 
+	enter_guest_mode(vcpu);
+
 	nested_svm_copy_common_state(svm->vmcb01.ptr, svm->nested.vmcb02.ptr);
 
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
@@ -1890,6 +1889,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	svm_copy_vmrun_state(&svm->vmcb01.ptr->save, save);
 	nested_copy_vmcb_control_to_cache(svm, ctl);
 
+	enter_guest_mode(vcpu);
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
 	nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip, svm->vmcb->save.cs.base);
 
-- 
2.53.0.rc2.204.g2597b5adb4-goog

Re: [PATCH v5 09/26] KVM: nSVM: Call enter_guest_mode() before switching to VMCB02

[Sean Christopherson]

On Fri, Feb 06, 2026, Yosry Ahmed wrote:
> In preparation for moving more changes that rely on is_guest_mode()
> before switching to VMCB02, move entering guest mode a bit earlier.
> 
> Nothing between the new callsite(s) and the old ones rely on
> is_guest_mode(), so this should be safe.
> 
> No functional change intended.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
>  arch/x86/kvm/svm/nested.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 29069fc5e8cb..607d99172e2b 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -741,9 +741,6 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  
>  	nested_svm_transition_tlb_flush(vcpu);
>  
> -	/* Enter Guest-Mode */
> -	enter_guest_mode(vcpu);
> -
>  	/*
>  	 * Filled at exit: exit_code, exit_info_1, exit_info_2, exit_int_info,
>  	 * exit_int_info_err, next_rip, insn_len, insn_bytes.
> @@ -944,6 +941,8 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
>  
>  	WARN_ON(svm->vmcb == svm->nested.vmcb02.ptr);
>  
> +	enter_guest_mode(vcpu);
> +
>  	nested_svm_copy_common_state(svm->vmcb01.ptr, svm->nested.vmcb02.ptr);
>  
>  	svm_switch_vmcb(svm, &svm->nested.vmcb02);
> @@ -1890,6 +1889,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>  	svm_copy_vmrun_state(&svm->vmcb01.ptr->save, save);
>  	nested_copy_vmcb_control_to_cache(svm, ctl);
>  
> +	enter_guest_mode(vcpu);
>  	svm_switch_vmcb(svm, &svm->nested.vmcb02);
>  	nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip, svm->vmcb->save.cs.base);


LOL, guess what!  Today end's in 'y', which means there's a nSVM bug!  It's a
super minor one though, especially in the broader context, I just happened to
see it when looking at this patch.

As per 3f6821aa147b ("KVM: x86: Forcibly leave nested if RSM to L2 hits shutdown"),
shutdown on RSM is suppose to hit L1, not L2.  But if enter_svm_guest_mode() fails,
svm_leave_smm() bails without leaving guest code.  Syzkaller probably hasn't found
the bug because nested_run_pending doesn't get set, but it's still technically
wrong.

Of course, as the comment in emulator_leave_smm() says, the *entire* RSM flow is
wrong, because it's not a VM-Enter/VMRUN, it's somethign else entirely.

Anyways, I don't think there's anything to do in this series, but at some point
we should probably do:

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index a2452b8ec49d..5cc9ad9b750d 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4877,13 +4877,15 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)
        vmcb12 = map.hva;
        nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
        nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
+
        ret = enter_svm_guest_mode(vcpu, smram64->svm_guest_vmcb_gpa, vmcb12, false);
-
        if (ret)
-               goto unmap_save;
+               goto leave_nested;
 
        svm->nested.nested_run_pending = 1;
 
+leave_nested:
+       svm_leave_nested(vcpu);
 unmap_save:
        kvm_vcpu_unmap(vcpu, &map_save);
 unmap_map:

Re: [PATCH v5 09/26] KVM: nSVM: Call enter_guest_mode() before switching to VMCB02

[Jim Mattson]

On Fri, Feb 20, 2026 at 5:13 PM Sean Christopherson <seanjc@google.com> wrote:
> LOL, guess what!  Today end's in 'y', which means there's a nSVM bug!  It's a
> super minor one though, especially in the broader context, I just happened to
> see it when looking at this patch.
>
> As per 3f6821aa147b ("KVM: x86: Forcibly leave nested if RSM to L2 hits shutdown"),
> shutdown on RSM is suppose to hit L1, not L2.  But if enter_svm_guest_mode() fails,
> svm_leave_smm() bails without leaving guest code.  Syzkaller probably hasn't found
> the bug because nested_run_pending doesn't get set, but it's still technically
> wrong.

Whoever came up with CONFIG_KVM_SMM was an absolute genius!

Re: [PATCH v5 09/26] KVM: nSVM: Call enter_guest_mode() before switching to VMCB02

[Yosry Ahmed]

[..] 
> LOL, guess what!  Today end's in 'y', which means there's a nSVM bug!  It's a
> super minor one though, especially in the broader context, I just happened to
> see it when looking at this patch.

LOL.

> 
> As per 3f6821aa147b ("KVM: x86: Forcibly leave nested if RSM to L2 hits shutdown"),
> shutdown on RSM is suppose to hit L1, not L2.  But if enter_svm_guest_mode() fails,
> svm_leave_smm() bails without leaving guest code.  Syzkaller probably hasn't found
> the bug because nested_run_pending doesn't get set, but it's still technically
> wrong.
> 
> Of course, as the comment in emulator_leave_smm() says, the *entire* RSM flow is
> wrong, because it's not a VM-Enter/VMRUN, it's somethign else entirely.
> 
> Anyways, I don't think there's anything to do in this series, but at some point
> we should probably do:

I would send a patch, but I have never tested (or did anything with) SMM
before, and I am trying to keep it that way :P

[PATCH v5 10/26] KVM: nSVM: Make nested_svm_merge_msrpm() return an errno

[Yosry Ahmed]

In preparation for moving nested_svm_merge_msrpm() within
enter_svm_guest_mode(), which returns an errno, return an errno from
nested_svm_merge_msrpm().

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 607d99172e2b..6e7238fed7ab 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -276,7 +276,7 @@ int __init nested_svm_init_msrpm_merge_offsets(void)
  * is optimized in that it only merges the parts where KVM MSR permission bitmap
  * may contain zero bits.
  */
-static bool nested_svm_merge_msrpm(struct kvm_vcpu *vcpu)
+static int nested_svm_merge_msrpm(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	nsvm_msrpm_merge_t *msrpm02 = svm->nested.msrpm;
@@ -303,17 +303,19 @@ static bool nested_svm_merge_msrpm(struct kvm_vcpu *vcpu)
 #endif
 
 	if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
-		return true;
+		return 0;
 
 	for (i = 0; i < nested_svm_nr_msrpm_merge_offsets; i++) {
 		const int p = nested_svm_msrpm_merge_offsets[i];
 		nsvm_msrpm_merge_t l1_val;
 		gpa_t gpa;
+		int r;
 
 		gpa = svm->nested.ctl.msrpm_base_pa + (p * sizeof(l1_val));
 
-		if (kvm_vcpu_read_guest(vcpu, gpa, &l1_val, sizeof(l1_val)))
-			return false;
+		r = kvm_vcpu_read_guest(vcpu, gpa, &l1_val, sizeof(l1_val));
+		if (r)
+			return r;
 
 		msrpm02[p] = msrpm01[p] | l1_val;
 	}
@@ -325,7 +327,7 @@ static bool nested_svm_merge_msrpm(struct kvm_vcpu *vcpu)
 #endif
 	svm->vmcb->control.msrpm_base_pa = __sme_set(__pa(svm->nested.msrpm));
 
-	return true;
+	return 0;
 }
 
 /*
@@ -1035,7 +1037,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 	if (enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12, true))
 		goto out_exit_err;
 
-	if (nested_svm_merge_msrpm(vcpu))
+	if (!nested_svm_merge_msrpm(vcpu))
 		goto out;
 
 out_exit_err:
@@ -1930,7 +1932,7 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 		if (CC(!load_pdptrs(vcpu, vcpu->arch.cr3)))
 			return false;
 
-	if (!nested_svm_merge_msrpm(vcpu)) {
+	if (nested_svm_merge_msrpm(vcpu)) {
 		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 		vcpu->run->internal.suberror =
 			KVM_INTERNAL_ERROR_EMULATION;
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 11/26] KVM: nSVM: Call nested_svm_merge_msrpm() from enter_svm_guest_mode()

[Yosry Ahmed]

In preparation for unifying the VMRUN failure code paths, move calling
nested_svm_merge_msrpm() into enter_svm_guest_mode() next to the
nested_svm_load_cr3() call (the other failure path in
enter_svm_guest_mode()).

Adding more uses of the from_vmrun parameter is not pretty, but it is
plumbed all the way to nested_svm_load_cr3() so it's not going away soon
anyway.

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 6e7238fed7ab..c16b68a07369 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -956,6 +956,12 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 	if (ret)
 		return ret;
 
+	if (from_vmrun) {
+		ret = nested_svm_merge_msrpm(vcpu);
+		if (ret)
+			return ret;
+	}
+
 	if (!from_vmrun)
 		kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
 
@@ -1034,22 +1040,17 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 
 	svm->nested.nested_run_pending = 1;
 
-	if (enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12, true))
-		goto out_exit_err;
-
-	if (!nested_svm_merge_msrpm(vcpu))
-		goto out;
-
-out_exit_err:
-	svm->nested.nested_run_pending = 0;
-	svm->nmi_l1_to_l2 = false;
-	svm->soft_int_injected = false;
+	if (enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12, true)) {
+		svm->nested.nested_run_pending = 0;
+		svm->nmi_l1_to_l2 = false;
+		svm->soft_int_injected = false;
 
-	svm->vmcb->control.exit_code    = SVM_EXIT_ERR;
-	svm->vmcb->control.exit_info_1  = 0;
-	svm->vmcb->control.exit_info_2  = 0;
+		svm->vmcb->control.exit_code    = SVM_EXIT_ERR;
+		svm->vmcb->control.exit_info_1  = 0;
+		svm->vmcb->control.exit_info_2  = 0;
 
-	nested_svm_vmexit(svm);
+		nested_svm_vmexit(svm);
+	}
 
 out:
 	kvm_vcpu_unmap(vcpu, &map);
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 12/26] KVM: nSVM: Call nested_svm_init_mmu_context() before switching to VMCB02

[Yosry Ahmed]

In preparation for moving more code that depends on
nested_svm_init_mmu_context() before switching to VMCB02, move the call
outside of nested_vmcb02_prepare_control() into callers, a bit earlier.
nested_svm_init_mmu_context() needs to be called after
enter_guest_mode(), but not after switching to VMCB02.

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index c16b68a07369..77cb98e39fb3 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -803,10 +803,6 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
 	/* Also overwritten later if necessary.  */
 	vmcb02->control.tlb_ctl = TLB_CONTROL_DO_NOTHING;
 
-	/* nested_cr3.  */
-	if (nested_npt_enabled(svm))
-		nested_svm_init_mmu_context(vcpu);
-
 	vcpu->arch.tsc_offset = kvm_calc_nested_tsc_offset(
 			vcpu->arch.l1_tsc_offset,
 			svm->nested.ctl.tsc_offset,
@@ -945,6 +941,9 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 
 	enter_guest_mode(vcpu);
 
+	if (nested_npt_enabled(svm))
+		nested_svm_init_mmu_context(vcpu);
+
 	nested_svm_copy_common_state(svm->vmcb01.ptr, svm->nested.vmcb02.ptr);
 
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
@@ -1893,6 +1892,10 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	nested_copy_vmcb_control_to_cache(svm, ctl);
 
 	enter_guest_mode(vcpu);
+
+	if (nested_npt_enabled(svm))
+		nested_svm_init_mmu_context(vcpu);
+
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
 	nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip, svm->vmcb->save.cs.base);
 
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 13/26] KVM: nSVM: Refactor minimal #VMEXIT handling out of nested_svm_vmexit()

[Yosry Ahmed]

In preparation for having a separate minimal #VMEXIT path for handling
failed VMRUNs, move the minimal logic out of nested_svm_vmexit() into a
helper.

This includes clearing the GIF, handling single-stepping on VMRUN, and a
few data structure cleanups.  Basically, everything that is required by
the architecture (or KVM) on a #VMEXIT where L2 never actually ran.

Additionally move uninitializing the nested MMU and reloading host CR3
to the new helper. It is not required at this point, but following
changes will require it.

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 61 ++++++++++++++++++++++-----------------
 1 file changed, 34 insertions(+), 27 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 77cb98e39fb3..a852508d7419 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -974,6 +974,34 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 	return 0;
 }
 
+static void __nested_svm_vmexit(struct vcpu_svm *svm)
+{
+	struct vmcb *vmcb01 = svm->vmcb01.ptr;
+	struct kvm_vcpu *vcpu = &svm->vcpu;
+
+	svm->nested.vmcb12_gpa = 0;
+	svm->nested.ctl.nested_cr3 = 0;
+
+	/* GIF is cleared on #VMEXIT, no event can be injected in L1 */
+	svm_set_gif(svm, false);
+	vmcb01->control.exit_int_info = 0;
+
+	nested_svm_uninit_mmu_context(vcpu);
+	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true)) {
+		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+		return;
+	}
+
+	/*
+	 * If we are here following the completion of a VMRUN that
+	 * is being single-stepped, queue the pending #DB intercept
+	 * right now so that it an be accounted for before we execute
+	 * L1's next instruction.
+	 */
+	if (unlikely(vmcb01->save.rflags & X86_EFLAGS_TF))
+		kvm_queue_exception(vcpu, DB_VECTOR);
+}
+
 int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -1121,8 +1149,6 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 	/* in case we halted in L2 */
 	kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
 
-	svm->nested.vmcb12_gpa = 0;
-
 	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map)) {
 		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 		return;
@@ -1239,13 +1265,6 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 		}
 	}
 
-	/*
-	 * On vmexit the  GIF is set to false and
-	 * no event can be injected in L1.
-	 */
-	svm_set_gif(svm, false);
-	vmcb01->control.exit_int_info = 0;
-
 	svm->vcpu.arch.tsc_offset = svm->vcpu.arch.l1_tsc_offset;
 	if (vmcb01->control.tsc_offset != svm->vcpu.arch.tsc_offset) {
 		vmcb01->control.tsc_offset = svm->vcpu.arch.tsc_offset;
@@ -1258,8 +1277,6 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 		svm_write_tsc_multiplier(vcpu);
 	}
 
-	svm->nested.ctl.nested_cr3 = 0;
-
 	/*
 	 * Restore processor state that had been saved in vmcb01
 	 */
@@ -1285,13 +1302,6 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 
 	nested_svm_transition_tlb_flush(vcpu);
 
-	nested_svm_uninit_mmu_context(vcpu);
-
-	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true)) {
-		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
-		return;
-	}
-
 	/*
 	 * Drop what we picked up for L2 via svm_complete_interrupts() so it
 	 * doesn't end up in L1.
@@ -1300,21 +1310,18 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 	kvm_clear_exception_queue(vcpu);
 	kvm_clear_interrupt_queue(vcpu);
 
-	/*
-	 * If we are here following the completion of a VMRUN that
-	 * is being single-stepped, queue the pending #DB intercept
-	 * right now so that it an be accounted for before we execute
-	 * L1's next instruction.
-	 */
-	if (unlikely(vmcb01->save.rflags & X86_EFLAGS_TF))
-		kvm_queue_exception(&(svm->vcpu), DB_VECTOR);
-
 	/*
 	 * Un-inhibit the AVIC right away, so that other vCPUs can start
 	 * to benefit from it right away.
 	 */
 	if (kvm_apicv_activated(vcpu->kvm))
 		__kvm_vcpu_update_apicv(vcpu);
+
+	/*
+	 * Potentially queues an exception, so it needs to be after
+	 * kvm_clear_exception_queue() is called above.
+	 */
+	__nested_svm_vmexit(svm);
 }
 
 static void nested_svm_triple_fault(struct kvm_vcpu *vcpu)
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 14/26] KVM: nSVM: Unify handling of VMRUN failures with proper cleanup

[Yosry Ahmed]

There are currently two possible causes of VMRUN failures emulated by
KVM:

1) Consistency checks failures. In this case, KVM updates the exit code
   in the mapped VMCB12 and exits early in nested_svm_vmrun(). This
   causes a few problems:

  A) KVM does not clear the GIF if the early consistency checks fail
     (because nested_svm_vmexit() is not called). Nothing requires
     GIF=0 before a VMRUN, from the APM:

	It is assumed that VMM software cleared GIF some time before
	executing the VMRUN instruction, to ensure an atomic state
	switch.

     So an early #VMEXIT from early consistency checks could leave the
     GIF set.

  B) svm_leave_smm() is missing consistency checks on the newly loaded
     guest state, because the checks aren't performed by
     enter_svm_guest_mode().

2) Failure to load L2's CR3 or merge the MSR bitmaps. In this case, a
   fully-fledged #VMEXIT injection is performed as VMCB02 is already
   prepared.

Arguably all VMRUN failures should be handled before the VMCB02 is
prepared, but with proper cleanup (e.g. clear the GIF). Move all the
potential failure checks inside enter_svm_guest_mode() before switching
to VMCB02. On failure of any of these checks, nested_svm_vmrun()
synthesizes a minimal #VMEXIT through the new nested_svm_failed_vmrun()
helper.

__nested_svm_vmexit() already performs the necessary cleanup for a
failed VMRUN, including uninitializing the nested MMU and reloading L1's
CR3. This ensures that consistency check failures do proper necessary
cleanup, while other failures do not doo too much cleanup. It also
leaves a unified path for handling VMRUN failures.

Cc: stable@vger.kernel.org
Fixes: 52c65a30a5c6 ("KVM: SVM: Check for nested vmrun intercept before emulating vmrun")
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 66 +++++++++++++++++++++++++--------------
 1 file changed, 42 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index a852508d7419..918f6a6eaf56 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -934,22 +934,19 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 				    vmcb12->control.intercepts[INTERCEPT_WORD4],
 				    vmcb12->control.intercepts[INTERCEPT_WORD5]);
 
-
 	svm->nested.vmcb12_gpa = vmcb12_gpa;
 
 	WARN_ON(svm->vmcb == svm->nested.vmcb02.ptr);
 
 	enter_guest_mode(vcpu);
 
+	if (!nested_vmcb_check_save(vcpu, &svm->nested.save) ||
+	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl))
+		return -EINVAL;
+
 	if (nested_npt_enabled(svm))
 		nested_svm_init_mmu_context(vcpu);
 
-	nested_svm_copy_common_state(svm->vmcb01.ptr, svm->nested.vmcb02.ptr);
-
-	svm_switch_vmcb(svm, &svm->nested.vmcb02);
-	nested_vmcb02_prepare_control(svm, vmcb12->save.rip, vmcb12->save.cs.base);
-	nested_vmcb02_prepare_save(svm, vmcb12);
-
 	ret = nested_svm_load_cr3(&svm->vcpu, svm->nested.save.cr3,
 				  nested_npt_enabled(svm), from_vmrun);
 	if (ret)
@@ -961,6 +958,17 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 			return ret;
 	}
 
+	/*
+	 * Any VMRUN failure needs to happen before this point, such that the
+	 * nested #VMEXIT is injected properly by nested_svm_vmrun_error_vmexit().
+	 */
+
+	nested_svm_copy_common_state(svm->vmcb01.ptr, svm->nested.vmcb02.ptr);
+
+	svm_switch_vmcb(svm, &svm->nested.vmcb02);
+	nested_vmcb02_prepare_control(svm, vmcb12->save.rip, vmcb12->save.cs.base);
+	nested_vmcb02_prepare_save(svm, vmcb12);
+
 	if (!from_vmrun)
 		kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
 
@@ -979,6 +987,8 @@ static void __nested_svm_vmexit(struct vcpu_svm *svm)
 	struct vmcb *vmcb01 = svm->vmcb01.ptr;
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 
+	WARN_ON_ONCE(is_guest_mode(vcpu));
+
 	svm->nested.vmcb12_gpa = 0;
 	svm->nested.ctl.nested_cr3 = 0;
 
@@ -1002,6 +1012,20 @@ static void __nested_svm_vmexit(struct vcpu_svm *svm)
 		kvm_queue_exception(vcpu, DB_VECTOR);
 }
 
+static void nested_svm_vmrun_error_vmexit(struct kvm_vcpu *vcpu, struct vmcb *vmcb12)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	WARN_ON_ONCE(svm->vmcb == svm->nested.vmcb02.ptr);
+
+	leave_guest_mode(vcpu);
+
+	vmcb12->control.exit_code = SVM_EXIT_ERR;
+	vmcb12->control.exit_info_1 = 0;
+	vmcb12->control.exit_info_2 = 0;
+	__nested_svm_vmexit(svm);
+}
+
 int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -1044,14 +1068,6 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 	nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
 	nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
 
-	if (!nested_vmcb_check_save(vcpu, &svm->nested.save) ||
-	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {
-		vmcb12->control.exit_code    = SVM_EXIT_ERR;
-		vmcb12->control.exit_info_1  = 0;
-		vmcb12->control.exit_info_2  = 0;
-		goto out;
-	}
-
 	/*
 	 * Since vmcb01 is not in use, we can use it to store some of the L1
 	 * state.
@@ -1072,14 +1088,9 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 		svm->nmi_l1_to_l2 = false;
 		svm->soft_int_injected = false;
 
-		svm->vmcb->control.exit_code    = SVM_EXIT_ERR;
-		svm->vmcb->control.exit_info_1  = 0;
-		svm->vmcb->control.exit_info_2  = 0;
-
-		nested_svm_vmexit(svm);
+		nested_svm_vmrun_error_vmexit(vcpu, vmcb12);
 	}
 
-out:
 	kvm_vcpu_unmap(vcpu, &map);
 
 	return ret;
@@ -1217,6 +1228,13 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_ERAPS))
 		vmcb01->control.erap_ctl |= ERAP_CONTROL_CLEAR_RAP;
 
+	/*
+	 * nested_svm_vmexit() is intended for use only when KVM is synthesizing
+	 * a #VMEXIT after a successful nested VMRUN.  All VMRUN consistency
+	 * checks must be performed before loading guest state, and so should
+	 * use __nested_svm_vmexit().
+	 */
+	WARN_ON_ONCE(svm->vmcb != svm->nested.vmcb02.ptr);
 	svm_switch_vmcb(svm, &svm->vmcb01);
 
 	/*
@@ -1903,9 +1921,6 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	if (nested_npt_enabled(svm))
 		nested_svm_init_mmu_context(vcpu);
 
-	svm_switch_vmcb(svm, &svm->nested.vmcb02);
-	nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip, svm->vmcb->save.cs.base);
-
 	/*
 	 * While the nested guest CR3 is already checked and set by
 	 * KVM_SET_SREGS, it was set when nested state was yet loaded,
@@ -1917,6 +1932,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	if (ret)
 		goto out_free;
 
+	svm_switch_vmcb(svm, &svm->nested.vmcb02);
+	nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip, svm->vmcb->save.cs.base);
+
 	svm->nested.force_msr_bitmap_recalc = true;
 
 	kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 15/26] KVM: nSVM: Clear EVENTINJ field in VMCB12 on nested #VMEXIT

[Yosry Ahmed]

According to the APM, from the reference of the VMRUN instruction:

	Upon #VMEXIT, the processor performs the following actions in
	order to return to the host execution context:
	...
	clear EVENTINJ field in VMCB

KVM correctly cleared EVENTINJ (i.e. event_inj and event_inj_err) on
nested #VMEXIT before commit 2d8a42be0e2b ("KVM: nSVM: synchronize VMCB
controls updated by the processor on every vmexit"). That commit made
sure the fields are synchronized between VMCB02 and KVM's cached VMCB12
on every L2->L0 #VMEXIT, such that they are serialized correctly on
save/restore.

However, the commit also incorrectly copied the fields from KVM's cached
VMCB12 to L1's VMCB12 on nested #VMEXIT. Go back to clearing the fields,
and so in __nested_svm_vmexit() instead of nested_svm_vmexit(), such
that it also applies to #VMEXITs caused by a failed VMRUN.

Fixes: 2d8a42be0e2b ("KVM: nSVM: synchronize VMCB controls updated by the processor on every vmexit")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 918f6a6eaf56..2f43b70930a8 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -982,7 +982,7 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 	return 0;
 }
 
-static void __nested_svm_vmexit(struct vcpu_svm *svm)
+static void __nested_svm_vmexit(struct vcpu_svm *svm, struct vmcb *vmcb12)
 {
 	struct vmcb *vmcb01 = svm->vmcb01.ptr;
 	struct kvm_vcpu *vcpu = &svm->vcpu;
@@ -996,6 +996,10 @@ static void __nested_svm_vmexit(struct vcpu_svm *svm)
 	svm_set_gif(svm, false);
 	vmcb01->control.exit_int_info = 0;
 
+	/* event_inj is cleared on #VMEXIT */
+	vmcb12->control.event_inj = 0;
+	vmcb12->control.event_inj_err = 0;
+
 	nested_svm_uninit_mmu_context(vcpu);
 	if (nested_svm_load_cr3(vcpu, vmcb01->save.cr3, false, true)) {
 		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
@@ -1023,7 +1027,7 @@ static void nested_svm_vmrun_error_vmexit(struct kvm_vcpu *vcpu, struct vmcb *vm
 	vmcb12->control.exit_code = SVM_EXIT_ERR;
 	vmcb12->control.exit_info_1 = 0;
 	vmcb12->control.exit_info_2 = 0;
-	__nested_svm_vmexit(svm);
+	__nested_svm_vmexit(svm, vmcb12);
 }
 
 int nested_svm_vmrun(struct kvm_vcpu *vcpu)
@@ -1205,8 +1209,6 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 		vmcb12->control.next_rip  = vmcb02->control.next_rip;
 
 	vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
-	vmcb12->control.event_inj         = svm->nested.ctl.event_inj;
-	vmcb12->control.event_inj_err     = svm->nested.ctl.event_inj_err;
 
 	if (!kvm_pause_in_guest(vcpu->kvm)) {
 		vmcb01->control.pause_filter_count = vmcb02->control.pause_filter_count;
@@ -1316,8 +1318,6 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 				       vmcb12->control.exit_int_info_err,
 				       KVM_ISA_SVM);
 
-	kvm_vcpu_unmap(vcpu, &map);
-
 	nested_svm_transition_tlb_flush(vcpu);
 
 	/*
@@ -1339,7 +1339,9 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 	 * Potentially queues an exception, so it needs to be after
 	 * kvm_clear_exception_queue() is called above.
 	 */
-	__nested_svm_vmexit(svm);
+	__nested_svm_vmexit(svm, vmcb12);
+
+	kvm_vcpu_unmap(vcpu, &map);
 }
 
 static void nested_svm_triple_fault(struct kvm_vcpu *vcpu)
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 16/26] KVM: nSVM: Drop the non-architectural consistency check for NP_ENABLE

[Yosry Ahmed]

KVM currenty fails a nested VMRUN and injects VMEXIT_INVALID (aka
SVM_EXIT_ERR) if L1 sets NP_ENABLE and the host does not support NPTs.
On first glance, it seems like the check should actually be for
guest_cpu_cap_has(X86_FEATURE_NPT) instead, as it is possible for the
host to support NPTs but the guest CPUID to not advertise it.

However, the consistency check is not architectural to begin with. The
APM does not mention VMEXIT_INVALID if NP_ENABLE is set on a processor
that does not have X86_FEATURE_NPT. Hence, NP_ENABLE should be ignored
if X86_FEATURE_NPT is not available for L1, so sanitize it when copying
from the VMCB12 to KVM's cache.

Apart from the consistency check, NP_ENABLE in VMCB12 is currently
ignored because the bit is actually copied from VMCB01 to VMCB02, not
from VMCB12.

Fixes: 4b16184c1cca ("KVM: SVM: Initialize Nested Nested MMU context on VMRUN")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 2f43b70930a8..61359e64e8ed 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -350,9 +350,6 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 	if (CC(control->asid == 0))
 		return false;
 
-	if (CC((control->nested_ctl & SVM_NESTED_CTL_NP_ENABLE) && !npt_enabled))
-		return false;
-
 	if (CC(!nested_svm_check_bitmap_pa(vcpu, control->msrpm_base_pa,
 					   MSRPM_SIZE)))
 		return false;
@@ -433,6 +430,11 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	nested_svm_sanitize_intercept(vcpu, to, SKINIT);
 	nested_svm_sanitize_intercept(vcpu, to, RDPRU);
 
+	/* Always clear SVM_NESTED_CTL_NP_ENABLE if the guest cannot use NPTs */
+	to->nested_ctl          = from->nested_ctl;
+	if (!guest_cpu_cap_has(vcpu, X86_FEATURE_NPT))
+		to->nested_ctl &= ~SVM_NESTED_CTL_NP_ENABLE;
+
 	to->iopm_base_pa        = from->iopm_base_pa;
 	to->msrpm_base_pa       = from->msrpm_base_pa;
 	to->tsc_offset          = from->tsc_offset;
@@ -446,7 +448,6 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	to->exit_info_2         = from->exit_info_2;
 	to->exit_int_info       = from->exit_int_info;
 	to->exit_int_info_err   = from->exit_int_info_err;
-	to->nested_ctl          = from->nested_ctl;
 	to->event_inj           = from->event_inj;
 	to->event_inj_err       = from->event_inj_err;
 	to->next_rip            = from->next_rip;
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 17/26] KVM: nSVM: Add missing consistency check for nCR3 validity

[Yosry Ahmed]

From the APM Volume #2, 15.25.4 (24593—Rev. 3.42—March 2024):

	When VMRUN is executed with nested paging enabled
	(NP_ENABLE = 1), the following conditions are considered illegal
	state combinations, in addition to those mentioned in
	“Canonicalization and Consistency Checks”:
	• Any MBZ bit of nCR3 is set.
	• Any G_PAT.PA field has an unsupported type encoding or any
	reserved field in G_PAT has a nonzero value.

Add the consistency check for nCR3 being a legal GPA with no MBZ bits
set. The G_PAT.PA check was proposed separately [*].

[*]https://lore.kernel.org/kvm/20260205214326.1029278-3-jmattson@google.com/

Fixes: 4b16184c1cca ("KVM: SVM: Initialize Nested Nested MMU context on VMRUN")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 61359e64e8ed..a5a5ce060f47 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -350,6 +350,11 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 	if (CC(control->asid == 0))
 		return false;
 
+	if (control->nested_ctl & SVM_NESTED_CTL_NP_ENABLE) {
+		if (CC(!kvm_vcpu_is_legal_gpa(vcpu, control->nested_cr3)))
+			return false;
+	}
+
 	if (CC(!nested_svm_check_bitmap_pa(vcpu, control->msrpm_base_pa,
 					   MSRPM_SIZE)))
 		return false;
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 18/26] KVM: nSVM: Add missing consistency check for hCR0.PG and NP_ENABLE

[Yosry Ahmed]

From the APM Volume #2, 15.25.3 (24593—Rev. 3.42—March 2024):

	If VMRUN is executed with hCR0.PG cleared to zero and NP_ENABLE
	set to 1 , VMRUN terminates with #VMEXIT(VMEXIT_INVALID).

Add the consistency check by plumbing L1's CR0 to
nested_vmcb_check_controls().

Fixes: 4b16184c1cca ("KVM: SVM: Initialize Nested Nested MMU context on VMRUN")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index a5a5ce060f47..ca2d1b1b8be6 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -342,7 +342,8 @@ static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa, u32 size)
 }
 
 static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
-				       struct vmcb_ctrl_area_cached *control)
+				       struct vmcb_ctrl_area_cached *control,
+				       unsigned long l1_cr0)
 {
 	if (CC(!vmcb12_is_intercept(control, INTERCEPT_VMRUN)))
 		return false;
@@ -353,6 +354,8 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 	if (control->nested_ctl & SVM_NESTED_CTL_NP_ENABLE) {
 		if (CC(!kvm_vcpu_is_legal_gpa(vcpu, control->nested_cr3)))
 			return false;
+		if (CC(!(l1_cr0 & X86_CR0_PG)))
+			return false;
 	}
 
 	if (CC(!nested_svm_check_bitmap_pa(vcpu, control->msrpm_base_pa,
@@ -947,7 +950,8 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 	enter_guest_mode(vcpu);
 
 	if (!nested_vmcb_check_save(vcpu, &svm->nested.save) ||
-	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl))
+	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl,
+					svm->vmcb01.ptr->save.cr0))
 		return -EINVAL;
 
 	if (nested_npt_enabled(svm))
@@ -1879,7 +1883,8 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 	ret = -EINVAL;
 	__nested_copy_vmcb_control_to_cache(vcpu, &ctl_cached, ctl);
-	if (!nested_vmcb_check_controls(vcpu, &ctl_cached))
+	/* 'save' contains L1 state saved from before VMRUN */
+	if (!nested_vmcb_check_controls(vcpu, &ctl_cached, save->cr0))
 		goto out_free;
 
 	/*
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 19/26] KVM: nSVM: Add missing consistency check for EFER, CR0, CR4, and CS

[Yosry Ahmed]

According to the APM Volume #2, 15.5, Canonicalization and Consistency
Checks (24593—Rev. 3.42—March 2024), the following condition (among
others) results in a #VMEXIT with VMEXIT_INVALID (aka SVM_EXIT_ERR):

  EFER.LME, CR0.PG, CR4.PAE, CS.L, and CS.D are all non-zero.

Add the missing consistency check. This is functionally a nop because
the nested VMRUN results in SVM_EXIT_ERR in HW, which is forwarded to
L1, but KVM makes all consistency checks before a VMRUN is actually
attempted.

Fixes: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 7 +++++++
 arch/x86/kvm/svm/svm.h    | 1 +
 2 files changed, 8 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index ca2d1b1b8be6..90942c8c9d9d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -397,6 +397,11 @@ static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
 		    CC(!(save->cr0 & X86_CR0_PE)) ||
 		    CC(!kvm_vcpu_is_legal_cr3(vcpu, save->cr3)))
 			return false;
+
+		if (CC((save->cr4 & X86_CR4_PAE) &&
+		       (save->cs.attrib & SVM_SELECTOR_L_MASK) &&
+		       (save->cs.attrib & SVM_SELECTOR_DB_MASK)))
+			return false;
 	}
 
 	/* Note, SVM doesn't have any additional restrictions on CR4. */
@@ -492,6 +497,8 @@ static void __nested_copy_vmcb_save_to_cache(struct vmcb_save_area_cached *to,
 	 * Copy only fields that are validated, as we need them
 	 * to avoid TOC/TOU races.
 	 */
+	to->cs = from->cs;
+
 	to->efer = from->efer;
 	to->cr0 = from->cr0;
 	to->cr3 = from->cr3;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 7629cb37c930..0a5d5a4453b7 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -140,6 +140,7 @@ struct kvm_vmcb_info {
 };
 
 struct vmcb_save_area_cached {
+	struct vmcb_seg cs;
 	u64 efer;
 	u64 cr4;
 	u64 cr3;
-- 
2.53.0.rc2.204.g2597b5adb4-goog

[PATCH v5 20/26] KVM: nSVM: Add missing consistency check for event_inj

[Yosry Ahmed]

According to the APM Volume #2, 15.20 (24593—Rev. 3.42—March 2024):

  VMRUN exits with VMEXIT_INVALID error code if either:
  • Reserved values of TYPE have been specified, or
  • TYPE = 3 (exception) has been specified with a vector that does not
    correspond to an exception (this includes vector 2, which is an NMI,
    not an exception).

Add the missing consistency checks to KVM. For the second point, inject
VMEXIT_INVALID if the vector is anything but the vectors defined by the
APM for exceptions. Reserved vectors are also considered invalid, which
matches the HW behavior. Vector 9 (i.e. #CSO) is considered invalid
because it is reserved on modern CPUs, and according to LLMs no CPUs
exist supporting SVM and producing #CSOs.

Defined exceptions could be different between virtual CPUs as new CPUs
define new vectors. In a best effort to dynamically define the valid
vectors, make all currently defined vectors as valid except those
obviously tied to a CPU feature: SHSTK -> #CP and SEV-ES -> #VC. As new
vectors are defined, they can similarly be tied to corresponding CPU
features.

Invalid vectors on specific (e.g. old) CPUs that are missed by KVM
should be rejected by HW anyway.

Fixes: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
CC: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
 arch/x86/kvm/svm/nested.c | 51 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 90942c8c9d9d..42f0dbd86a89 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -341,6 +341,54 @@ static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa, u32 size)
 	    kvm_vcpu_is_legal_gpa(vcpu, addr + size - 1);
 }
 
+static bool nested_svm_event_inj_valid_exept(struct kvm_vcpu *vcpu, u8 vector)
+{
+	/*
+	 * Vectors that do not correspond to a defined exception are invalid
+	 * (including #NMI and reserved vectors). In a best effort to define
+	 * valid exceptions based on the virtual CPU, make all exceptions always
+	 * valid except those obviously tied to a CPU feature.
+	 */
+	switch (vector) {
+	case DE_VECTOR: case DB_VECTOR: case BP_VECTOR: case OF_VECTOR:
+	case BR_VECTOR: case UD_VECTOR: case NM_VECTOR: case DF_VECTOR:
+	case TS_VECTOR: case NP_VECTOR: case SS_VECTOR: case GP_VECTOR:
+	case PF_VECTOR: case MF_VECTOR: case AC_VECTOR: case MC_VECTOR:
+	case XM_VECTOR: case HV_VECTOR: case SX_VECTOR:
+		return true;
+	case CP_VECTOR:
+		return guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
+	case VC_VECTOR:
+		return guest_cpu_cap_has(vcpu, X86_FEATURE_SEV_ES);
+	}
+	return false;
+}
+
+/*
+ * According to the APM, VMRUN exits with SVM_EXIT_ERR if SVM_EVTINJ_VALID is
+ * set and:
+ * - The type of event_inj is not one of the defined values.
+ * - The type is SVM_EVTINJ_TYPE_EXEPT, but the vector is not a valid exception.
+ */
+static bool nested_svm_check_event_inj(struct kvm_vcpu *vcpu, u32 event_inj)
+{
+	u32 type = event_inj & SVM_EVTINJ_TYPE_MASK;
+	u8 vector = event_inj & SVM_EVTINJ_VEC_MASK;
+
+	if (!(event_inj & SVM_EVTINJ_VALID))
+		return true;
+
+	if (type != SVM_EVTINJ_TYPE_INTR && type != SVM_EVTINJ_TYPE_NMI &&
+	    type != SVM_EVTINJ_TYPE_EXEPT && type != SVM_EVTINJ_TYPE_SOFT)
+		return false;
+
+	if (type == SVM_EVTINJ_TYPE_EXEPT &&
+	    !nested_svm_event_inj_valid_exept(vcpu, vector))
+		return false;
+
+	return true;
+}
+
 static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 				       struct vmcb_ctrl_area_cached *control,
 				       unsigned long l1_cr0)
@@ -370,6 +418,9 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 		return false;
 	}
 
+	if (CC(!nested_svm_check_event_inj(vcpu, control->event_inj)))
+		return false;
+
 	return true;
 }
 
-- 
2.53.0.rc2.204.g2597b5adb4-goog