[PATCH v2 0/3] KVM: nSVM: fix #TF from CR3 switch when entering guest

[PATCH v2 0/3] KVM: nSVM: fix #TF from CR3 switch when entering guest

[Vitaly Kuznetsov]

This is a succesor of "[PATCH] KVM: x86: drop erroneous mmu_check_root()
from fast_pgd_switch()".

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().

Fix the issue by moving kvm_mmu_new_pgd() to the right place when switching
to nested guest and drop the unneeded mmu_check_root() check from
fast_pgd_switch().

Vitaly Kuznetsov (3):
  KVM: nSVM: split kvm_init_shadow_npt_mmu() from kvm_init_shadow_mmu()
  KVM: nSVM: properly call kvm_mmu_new_pgd() upon switching to guest
  KVM: x86: drop superfluous mmu_check_root() from fast_pgd_switch()

 arch/x86/include/asm/kvm_host.h |  7 ++++++-
 arch/x86/kvm/mmu.h              |  3 ++-
 arch/x86/kvm/mmu/mmu.c          | 36 ++++++++++++++++++++++++---------
 arch/x86/kvm/svm/nested.c       |  5 +++--
 arch/x86/kvm/x86.c              |  8 +++++---
 5 files changed, 43 insertions(+), 16 deletions(-)

-- 
2.25.4

[PATCH v2 1/3] KVM: nSVM: split kvm_init_shadow_npt_mmu() from kvm_init_shadow_mmu()

[Vitaly Kuznetsov]

As a preparatory change for moving kvm_mmu_new_pgd() from
nested_prepare_vmcb_save() to nested_svm_init_mmu_context() split
kvm_init_shadow_npt_mmu() from kvm_init_shadow_mmu(). This also makes
the code look more like nVMX (kvm_init_shadow_ept_mmu()).

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/mmu.h        |  3 ++-
 arch/x86/kvm/mmu/mmu.c    | 31 ++++++++++++++++++++++++-------
 arch/x86/kvm/svm/nested.c |  3 ++-
 3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 444bb9c54548..94378ef1df54 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -57,7 +57,8 @@ void
 reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
 
 void kvm_init_mmu(struct kvm_vcpu *vcpu, bool reset_roots);
-void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer);
+void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer,
+			     gpa_t nested_cr3);
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
 			     bool accessed_dirty, gpa_t new_eptp);
 bool kvm_can_do_async_pf(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 76817d13c86e..167d12ab957a 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4952,14 +4952,10 @@ kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu, bool base_only)
 	return role;
 }
 
-void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer)
+static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4,
+				    u32 efer, union kvm_mmu_role new_role)
 {
 	struct kvm_mmu *context = vcpu->arch.mmu;
-	union kvm_mmu_role new_role =
-		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
-
-	if (new_role.as_u64 == context->mmu_role.as_u64)
-		return;
 
 	if (!(cr0 & X86_CR0_PG))
 		nonpaging_init_context(vcpu, context);
@@ -4973,7 +4969,28 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer)
 	context->mmu_role.as_u64 = new_role.as_u64;
 	reset_shadow_zero_bits_mask(vcpu, context);
 }
-EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);
+
+static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer)
+{
+	struct kvm_mmu *context = vcpu->arch.mmu;
+	union kvm_mmu_role new_role =
+		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
+
+	if (new_role.as_u64 != context->mmu_role.as_u64)
+		shadow_mmu_init_context(vcpu, cr0, cr4, efer, new_role);
+}
+
+void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer,
+			     gpa_t nested_cr3)
+{
+	struct kvm_mmu *context = vcpu->arch.mmu;
+	union kvm_mmu_role new_role =
+		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
+
+	if (new_role.as_u64 != context->mmu_role.as_u64)
+		shadow_mmu_init_context(vcpu, cr0, cr4, efer, new_role);
+}
+EXPORT_SYMBOL_GPL(kvm_init_shadow_npt_mmu);
 
 static union kvm_mmu_role
 kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty,
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 6bceafb19108..e424bce13e6c 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -87,7 +87,8 @@ static void nested_svm_init_mmu_context(struct kvm_vcpu *vcpu)
 	WARN_ON(mmu_is_nested(vcpu));
 
 	vcpu->arch.mmu = &vcpu->arch.guest_mmu;
-	kvm_init_shadow_mmu(vcpu, X86_CR0_PG, hsave->save.cr4, hsave->save.efer);
+	kvm_init_shadow_npt_mmu(vcpu, X86_CR0_PG, hsave->save.cr4, hsave->save.efer,
+				svm->nested.ctl.nested_cr3);
 	vcpu->arch.mmu->get_guest_pgd     = nested_svm_get_tdp_cr3;
 	vcpu->arch.mmu->get_pdptr         = nested_svm_get_tdp_pdptr;
 	vcpu->arch.mmu->inject_page_fault = nested_svm_inject_npf_exit;
-- 
2.25.4

[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@redhat.com>
---
 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

[PATCH v2 3/3] KVM: x86: drop superfluous mmu_check_root() from fast_pgd_switch()

[Vitaly Kuznetsov]

The mmu_check_root() check in fast_pgd_switch() seems to be
superfluous: when GPA is outside of the visible range
cached_root_available() will fail for non-direct roots
(as we can't have a matching one on the list) and we don't
seem to care for direct ones.

Also, raising #TF immediately when a non-existent GFN is written to CR3
doesn't seem to mach architectural behavior. Drop the check.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ebf0cb3f1ce0..16c7701f1741 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4277,8 +4277,7 @@ static bool fast_pgd_switch(struct kvm_vcpu *vcpu, gpa_t new_pgd,
 	 */
 	if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL &&
 	    mmu->root_level >= PT64_ROOT_4LEVEL)
-		return !mmu_check_root(vcpu, new_pgd >> PAGE_SHIFT) &&
-		       cached_root_available(vcpu, new_pgd, new_role);
+		return cached_root_available(vcpu, new_pgd, new_role);
 
 	return false;
 }
-- 
2.25.4

Re: [PATCH v2 1/3] KVM: nSVM: split kvm_init_shadow_npt_mmu() from kvm_init_shadow_mmu()

[Paolo Bonzini]

On 08/07/20 11:36, Vitaly Kuznetsov wrote:
> @@ -4973,7 +4969,28 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer)
>  	context->mmu_role.as_u64 = new_role.as_u64;
>  	reset_shadow_zero_bits_mask(vcpu, context);
>  }
> -EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);
> +
> +static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer)
> +{
> +	struct kvm_mmu *context = vcpu->arch.mmu;
> +	union kvm_mmu_role new_role =
> +		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
> +
> +	if (new_role.as_u64 != context->mmu_role.as_u64)
> +		shadow_mmu_init_context(vcpu, cr0, cr4, efer, new_role);
> +}
> +
> +void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer,
> +			     gpa_t nested_cr3)
> +{
> +	struct kvm_mmu *context = vcpu->arch.mmu;
> +	union kvm_mmu_role new_role =
> +		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
> +
> +	if (new_role.as_u64 != context->mmu_role.as_u64)
> +		shadow_mmu_init_context(vcpu, cr0, cr4, efer, new_role);
> +}
> +EXPORT_SYMBOL_GPL(kvm_init_shadow_npt_mmu);
>  
>  static union kvm_mmu_role

As a follow up, the assignments to context should stop using
vcpu->arch.mmu in favor of root_mmu/guest_mmu.

Paolo

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

[Paolo Bonzini]

On 08/07/20 11:36, Vitaly Kuznetsov wrote:
> 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@redhat.com>
> ---
>  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)
>  {
> 

Instead of the new argument (which is not really named right since it's
never true for !NPT) you could perhaps check vcpu->arch.mmu.  But also,
for NPT=1 the kvm_mmu_new_pgd is also unnecessary on vmexit, because the
old roots are still valid (or has been invalidated otherwise) while L2
was running.

I'm also not sure if skip_tlb_flush can use X86_CR3_PCID_NOFLUSH the way
kvm_set_cr3 does, so I wouldn't mind duplicating the code completely as
is already the case for nested_vmx_load_cr3.  It would introduce some
code duplication, but overall the code would be better.  For now, there
need not be an equivalent to nested_vmx_transition_mmu_sync, ASID
handling can be left for later.

Paolo

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

[Vitaly Kuznetsov]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 08/07/20 11:36, Vitaly Kuznetsov wrote:
>> 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@redhat.com>
>> ---
>>  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)
>>  {
>> 
>
> Instead of the new argument (which is not really named right since it's
> never true for !NPT) you could perhaps check vcpu->arch.mmu.  But also,
> for NPT=1 the kvm_mmu_new_pgd is also unnecessary on vmexit, because the
> old roots are still valid (or has been invalidated otherwise) while L2
> was running.
>
> I'm also not sure if skip_tlb_flush can use X86_CR3_PCID_NOFLUSH the way
> kvm_set_cr3 does, so I wouldn't mind duplicating the code completely as
> is already the case for nested_vmx_load_cr3.  It would introduce some
> code duplication, but overall the code would be better.  For now, there
> need not be an equivalent to nested_vmx_transition_mmu_sync, ASID
> handling can be left for later.

Sounds reasonable,

let's introduce nested_svm_load_cr3() to not mix these two concepts
together. I'll be back with v3 shortly, thanks!

-- 
Vitaly