[PATCH v8 4/8] KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT

Jim Mattson
2026-04-07T19:03:54Z

When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled and nested NPT is
enabled in vmcb12, copy the (cached and validated) vmcb12 g_pat field to
vmcb02's g_pat, giving L2 its own independent guest PAT register.

When the quirk is enabled (default), or when NPT is enabled but nested NPT
is disabled, copy L1's IA32_PAT MSR to the vmcb02 g_pat field, since L2
shares the IA32_PAT MSR with L1.

When NPT is disabled, the g_pat field is ignored by hardware.

Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
Signed-off-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/svm/nested.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 515a8545e8e0..58574e803812 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -727,9 +727,6 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm)
struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
struct kvm_vcpu *vcpu = &svm->vcpu;

- nested_vmcb02_compute_g_pat(svm);
- vmcb_mark_dirty(vmcb02, VMCB_NPT);
-
/* Load the nested guest state */
if (svm->nested.vmcb12_gpa != svm->nested.last_vmcb12_gpa) {
new_vmcb12 = true;
@@ -760,6 +757,13 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm)
vmcb_mark_dirty(vmcb02, VMCB_CET);
}

+ if (l2_has_separate_pat(vcpu)) {
+ if (unlikely(new_vmcb12 || vmcb12_is_dirty(control, VMCB_NPT)))
+ vmcb_set_gpat(vmcb02, svm->nested.save.g_pat);
+ } else if (npt_enabled) {
+ vmcb_set_gpat(vmcb02, vcpu->arch.pat);
+ }
+
kvm_set_rflags(vcpu, save->rflags | X86_EFLAGS_FIXED);

svm_set_efer(vcpu, svm->nested.save.efer);
--
2.53.0.1213.gd9a14994de-goog