[PATCH v2 2/3] KVM: nSVM: properly call kvm_mmu_new_pgd() upon switching to guest

[Vitaly Kuznetsov]

Undesired triple fault gets injected to L1 guest on SVM when L2 is
launched with certain CR3 values. #TF is raised by mmu_check_root()
check in fast_pgd_switch() and the root cause is that when
kvm_set_cr3() is called from nested_prepare_vmcb_save() with NPT
enabled CR3 points to a nGPA so we can't check it with
kvm_is_visible_gfn().

Calling kvm_mmu_new_pgd() with L2's CR3 idea when NPT is in use
seems to be wrong, an acceptable place for it seems to be
kvm_init_shadow_npt_mmu(). This also matches nVMX code.

Fixes: 7c390d350f8b ("kvm: x86: Add fast CR3 switch code path")
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 7 ++++++-
 arch/x86/kvm/mmu/mmu.c          | 2 ++
 arch/x86/kvm/svm/nested.c       | 2 +-
 arch/x86/kvm/x86.c              | 8 +++++---
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index be5363b21540..49b62f024f51 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1459,7 +1459,12 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
 		    int reason, bool has_error_code, u32 error_code);
 
 int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
-int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);
+int __kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool cr3_is_nested);
+static inline int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
+{
+	return __kvm_set_cr3(vcpu, cr3, false);
+}
+
 int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
 int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 167d12ab957a..ebf0cb3f1ce0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4987,6 +4987,8 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer,
 	union kvm_mmu_role new_role =
 		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
 
+	__kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base, true, true);
+
 	if (new_role.as_u64 != context->mmu_role.as_u64)
 		shadow_mmu_init_context(vcpu, cr0, cr4, efer, new_role);
 }
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index e424bce13e6c..b467917a9784 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -324,7 +324,7 @@ static void nested_prepare_vmcb_save(struct vcpu_svm *svm, struct vmcb *nested_v
 	svm_set_efer(&svm->vcpu, nested_vmcb->save.efer);
 	svm_set_cr0(&svm->vcpu, nested_vmcb->save.cr0);
 	svm_set_cr4(&svm->vcpu, nested_vmcb->save.cr4);
-	(void)kvm_set_cr3(&svm->vcpu, nested_vmcb->save.cr3);
+	(void)__kvm_set_cr3(&svm->vcpu, nested_vmcb->save.cr3, npt_enabled);
 
 	svm->vmcb->save.cr2 = svm->vcpu.arch.cr2 = nested_vmcb->save.cr2;
 	kvm_rax_write(&svm->vcpu, nested_vmcb->save.rax);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3b92db412335..3761135eb052 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1004,7 +1004,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 }
 EXPORT_SYMBOL_GPL(kvm_set_cr4);
 
-int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
+int __kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool cr3_is_nested)
 {
 	bool skip_tlb_flush = false;
 #ifdef CONFIG_X86_64
@@ -1031,13 +1031,15 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 		 !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
 		return 1;
 
-	kvm_mmu_new_pgd(vcpu, cr3, skip_tlb_flush, skip_tlb_flush);
+	if (!cr3_is_nested)
+		kvm_mmu_new_pgd(vcpu, cr3, skip_tlb_flush, skip_tlb_flush);
+
 	vcpu->arch.cr3 = cr3;
 	kvm_register_mark_available(vcpu, VCPU_EXREG_CR3);
 
 	return 0;
 }
-EXPORT_SYMBOL_GPL(kvm_set_cr3);
+EXPORT_SYMBOL_GPL(__kvm_set_cr3);
 
 int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
 {
-- 
2.25.4