Re: [PATCH 22/22] KVM: nSVM: enable GMET for guests

[Nikunj A. Dadhania]

On 3/25/2026 1:27 AM, Jon Kohler wrote:
> 
> 
>> On Mar 20, 2026, at 8:09 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>
>> All that needs to be done is moving the GMET bit from vmcs12 to
>> vmcs02.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/svm/nested.c | 3 +++
>> arch/x86/kvm/svm/svm.c    | 3 +++
>> 2 files changed, 6 insertions(+)
>>
>> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
>> index d69bcf52f948..397e9afecb78 100644
>> --- a/arch/x86/kvm/svm/nested.c
>> +++ b/arch/x86/kvm/svm/nested.c
>> @@ -774,6 +774,9 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>> vmcb02->control.bus_lock_counter = 0;
>>
>> vmcb02->control.nested_ctl &= ~SVM_NESTED_CTL_GMET_ENABLE;
>> + if (guest_cpu_cap_has(vcpu, X86_FEATURE_GMET))
>> + vmcb02->control.nested_ctl |=
>> + (svm->nested.ctl.nested_ctl & SVM_NESTED_CTL_GMET_ENABLE);
>>
>> /* Done at vmrun: asid.  */
>>
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index d3b69eb3242b..4a0d97e70dc2 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -5294,6 +5294,9 @@ static __init void svm_set_cpu_caps(void)
>> if (boot_cpu_has(X86_FEATURE_PFTHRESHOLD))
>> kvm_cpu_cap_set(X86_FEATURE_PFTHRESHOLD);
>>
>> + if (boot_cpu_has(X86_FEATURE_GMET))
>> + kvm_cpu_cap_set(X86_FEATURE_GMET);
>> +
>> if (vgif)
>> kvm_cpu_cap_set(X86_FEATURE_VGIF);
>>
>> -- 
>> 2.52.0
>>
> 
> When I enable gmet on the guest, and try to boot with memory integrity
> enabled in Windows 11 25H2 guest, the machine does not boot, but rather
> gets stuck in an NPF loop and does not make any progress.

Same here as well, trying to debug

  kvm_nested_vmenter: rip: 0xfffff8148793c2ea vmcb: 0x00000001087fd000 nested_rip: 0xfffff81487993d90 int_ctl: 0x00000000 event_inj: 0x00000000 nested_npt=n guest_cr3: 0x00000001087ce000
  kvm_nested_vmexit: vcpu 0 reason npf rip 0xfffff81487993d90 info1 0x0000000200000006 info2 0x00000001087cef80 intr_info 0x00000000 error_code 0x00000000 requests 0x0000000000000000

This seems to be the first entry into the nested guest and nested page fault is on guest_cr3 page

  kvm_mmu_set_spte: gfn 108600 spte 39ac00ee3 (rwx-) level 2 at 3012b1218

A 2M page is provisioned in the NPT

  kvm_nested_vmexit: vcpu 0 reason npf rip 0xfffff81487993d90 info1 0x0000000200000007 info2 0x00000001087cef80 intr_info 0x00000000 error_code 0x00000000 requests 0x0000000000000000

But the fault keeps hitting.