[v4] KVM: x86: nSVM: Improve PAT virtualization

[PATCH v4 5/8] KVM: x86: nSVM: Save gPAT to vmcb12.g_pat on VMEXIT

Posted by Jim Mattson 1 month, 2 weeks ago

According to the APM volume 3 pseudo-code for "VMRUN," when nested paging
is enabled in the vmcb, the guest PAT register (gPAT) is saved to the vmcb
on emulated VMEXIT.

When nested NPT is enabled, save the vmcb02 g_pat field to the vmcb12 g_pat
field on emulated VMEXIT.

Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/svm/nested.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 69b577a4915c..26f758e294ab 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1312,6 +1312,9 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
 	vmcb12->save.dr6    = svm->vcpu.arch.dr6;
 	vmcb12->save.cpl    = vmcb02->save.cpl;
 
+	if (nested_npt_enabled(svm))
+		vmcb12->save.g_pat = vmcb02->save.g_pat;
+
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
 		vmcb12->save.s_cet	= vmcb02->save.s_cet;
 		vmcb12->save.isst_addr	= vmcb02->save.isst_addr;
-- 
2.53.0.239.g8d8fc8a987-goog

Re: [PATCH v4 5/8] KVM: x86: nSVM: Save gPAT to vmcb12.g_pat on VMEXIT

Posted by Yosry Ahmed 1 month, 2 weeks ago

On Thu, Feb 12, 2026 at 07:58:53AM -0800, Jim Mattson wrote:
> According to the APM volume 3 pseudo-code for "VMRUN," when nested paging
> is enabled in the vmcb, the guest PAT register (gPAT) is saved to the vmcb
> on emulated VMEXIT.
> 
> When nested NPT is enabled, save the vmcb02 g_pat field to the vmcb12 g_pat
> field on emulated VMEXIT.
> 
> Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
> Signed-off-by: Jim Mattson <jmattson@google.com>

Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>

> ---
>  arch/x86/kvm/svm/nested.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 69b577a4915c..26f758e294ab 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1312,6 +1312,9 @@ void nested_svm_vmexit(struct vcpu_svm *svm)
>  	vmcb12->save.dr6    = svm->vcpu.arch.dr6;
>  	vmcb12->save.cpl    = vmcb02->save.cpl;
>  
> +	if (nested_npt_enabled(svm))
> +		vmcb12->save.g_pat = vmcb02->save.g_pat;
> +
>  	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
>  		vmcb12->save.s_cet	= vmcb02->save.s_cet;
>  		vmcb12->save.isst_addr	= vmcb02->save.isst_addr;
> -- 
> 2.53.0.239.g8d8fc8a987-goog
>