[PATCH v4 3/8] KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT

[Jim Mattson]

When nested NPT is enabled in vmcb12, copy the (cached and validated)
vmcb12 g_pat field to the guest PAT register. Under KVM, the guest PAT
register lives in svm->nested.save.g_pat.

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 <jmatt...@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 91b35adb83f8..dc8275837120 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -724,9 +724,6 @@ 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;
@@ -757,6 +754,13 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm 
*svm)
                vmcb_mark_dirty(vmcb02, VMCB_CET);
        }
 
+       if (nested_npt_enabled(svm)) {
+               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);
-- 
2.53.0.239.g8d8fc8a987-goog