[PATCH 28/28] KVM: nSVM: enable GMET for guests

Paolo Bonzini
2026-04-30T15:08:19Z

All that needs to be done is moving the GMET bit from vmcb12 to vmcb02.
The only new thing is that __nested_copy_vmcb_control_to_cache now
ensures that ignored-if-unavailable bits are zero in svm->nested.ctl.

Tested-by: David Riley <d.riley@proxmox.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/svm/nested.c | 6 +++++-
arch/x86/kvm/svm/svm.c | 3 +++
2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 74a1df1cb84f..3d1fd1776e19 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -489,11 +489,14 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
nested_svm_sanitize_intercept(vcpu, to, SKINIT);
nested_svm_sanitize_intercept(vcpu, to, RDPRU);

- /* Always clear SVM_MISC_ENABLE_NP if the guest cannot use NPTs */
+ /* Always clear misc_ctl bits that the guest cannot use */
to->misc_ctl = from->misc_ctl;
if (!guest_cpu_cap_has(vcpu, X86_FEATURE_NPT))
to->misc_ctl &= ~SVM_MISC_ENABLE_NP;

+ if (!gmet_enabled || !guest_cpu_cap_has(vcpu, X86_FEATURE_GMET))
+ to->misc_ctl &= ~SVM_MISC_ENABLE_GMET;
+
to->iopm_base_pa = from->iopm_base_pa & PAGE_MASK;
to->msrpm_base_pa = from->msrpm_base_pa & PAGE_MASK;
to->tsc_offset = from->tsc_offset;
@@ -898,6 +901,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
/* Use vmcb01 MMU and format if guest does not use nNPT */
if (nested_npt_enabled(svm)) {
vmcb02->control.misc_ctl &= ~SVM_MISC_ENABLE_GMET;
+ vmcb02->control.misc_ctl |= (svm->nested.ctl.misc_ctl & SVM_MISC_ENABLE_GMET);

nested_svm_init_mmu_context(vcpu);
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fd79874c5f4b..a82471a6d3ea 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5504,6 +5504,9 @@ static __init void svm_set_cpu_caps(void)
if (boot_cpu_has(X86_FEATURE_PFTHRESHOLD))
kvm_cpu_cap_set(X86_FEATURE_PFTHRESHOLD);

+ if (gmet_enabled)
+ kvm_cpu_cap_set(X86_FEATURE_GMET);
+
if (vgif)
kvm_cpu_cap_set(X86_FEATURE_VGIF);

--
2.52.0