[PATCH v7 2/9] KVM: x86: nSVM: Clear VMCB_NPT clean bit when updating hPAT from guest mode

Jim Mattson
2026-03-27T23:40:32Z

When running an L2 guest and writing to MSR_IA32_CR_PAT, the host PAT value
is stored in both vmcb01's g_pat field and vmcb02's g_pat field, but the
clean bit was only being cleared for vmcb02.

Introduce the helper vmcb_set_gpat() which sets vmcb->save.g_pat and marks
the VMCB dirty for VMCB_NPT. Use this helper in both svm_set_msr() for
updating vmcb01 and in nested_vmcb02_compute_g_pat() for updating vmcb02,
ensuring both VMCBs' NPT fields are properly marked dirty.

Fixes: 4995a3685f1b ("KVM: SVM: Use a separate vmcb for the nested L2 guest")
Signed-off-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/svm/nested.c | 2 +-
arch/x86/kvm/svm/svm.c | 3 +--
arch/x86/kvm/svm/svm.h | 6 ++++++
3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 5ff01d2ac85e..32fa8e688c00 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -697,7 +697,7 @@ void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm)
return;

/* FIXME: merge g_pat from vmcb01 and vmcb12. */
- svm->nested.vmcb02.ptr->save.g_pat = svm->vmcb01.ptr->save.g_pat;
+ vmcb_set_gpat(svm->nested.vmcb02.ptr, svm->vmcb01.ptr->save.g_pat);
}

static bool nested_vmcb12_has_lbrv(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d2ca226871c2..af808e83173e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2979,10 +2979,9 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
if (ret)
break;

- svm->vmcb01.ptr->save.g_pat = data;
+ vmcb_set_gpat(svm->vmcb01.ptr, data);
if (is_guest_mode(vcpu))
nested_vmcb02_compute_g_pat(svm);
- vmcb_mark_dirty(svm->vmcb, VMCB_NPT);
break;
case MSR_IA32_SPEC_CTRL:
if (!msr->host_initiated &&
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 74014110b550..a1d62c3cc3d6 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -439,6 +439,12 @@ static inline bool vmcb12_is_dirty(struct vmcb_ctrl_area_cached *control, int bi
return !test_bit(bit, (unsigned long *)&control->clean);
}

+static inline void vmcb_set_gpat(struct vmcb *vmcb, u64 data)
+{
+ vmcb->save.g_pat = data;
+ vmcb_mark_dirty(vmcb, VMCB_NPT);
+}
+
static __always_inline struct vcpu_svm *to_svm(struct kvm_vcpu *vcpu)
{
return container_of(vcpu, struct vcpu_svm, vcpu);
--
2.53.0.1018.g2bb0e51243-goog