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KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE

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Add a 'gpat' field to kvm_svm_nested_state_hdr to carry L2's guest PAT
value across save and restore.

When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled and the vCPU is in
guest mode with nested NPT enabled, save vmcb02's g_pat into the header on
KVM_GET_NESTED_STATE, and restore it on KVM_SET_NESTED_STATE.

Host-initiated accesses to IA32_PAT (via KVM_GET/SET_MSRS) always target
L1's hPAT, so they cannot be used to save or restore gPAT. The separate
header field ensures that KVM_GET/SET_MSRS and KVM_GET/SET_NESTED_STATE are
independent and can be ordered arbitrarily during save and restore.

Note that struct kvm_svm_nested_state_hdr is included in a union padded to
120 bytes, so there is room to add the gpat field without changing any
offsets.

Fixes: cc440cdad5 ("KVM: nSVM: implement KVM_GET_NESTED_STATE and KVM_SET_NESTED_STATE")
Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20260407190343.325299-9-jmattson@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Jim Mattson 2026-04-07 12:03:31 -07:00 committed by Sean Christopherson
parent 32ebdbce3b
commit 4f256d5770
3 changed files with 21 additions and 0 deletions
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1
Documentation/virt/kvm/api.rst
View File

@ -4967,6 +4967,7 @@ Errors:
struct kvm_svm_nested_state_hdr {
__u64 vmcb_pa;
__u64 gpat;
};
struct kvm_vmx_nested_state_data {

1
arch/x86/include/uapi/asm/kvm.h
View File

@ -533,6 +533,7 @@ struct kvm_svm_nested_state_data {
struct kvm_svm_nested_state_hdr {
__u64 vmcb_pa;
__u64 gpat;
};
/* for KVM_CAP_NESTED_STATE */

19
arch/x86/kvm/svm/nested.c
View File

@ -1876,6 +1876,9 @@ static int svm_get_nested_state(struct kvm_vcpu *vcpu,
/* First fill in the header and copy it out. */
if (is_guest_mode(vcpu)) {
kvm_state.hdr.svm.vmcb_pa = svm->nested.vmcb12_gpa;
kvm_state.hdr.svm.gpat = 0;
if (l2_has_separate_pat(vcpu))
kvm_state.hdr.svm.gpat = svm->vmcb->save.g_pat;
kvm_state.size += KVM_STATE_NESTED_SVM_VMCB_SIZE;
kvm_state.flags |= KVM_STATE_NESTED_GUEST_MODE;
@ -1928,6 +1931,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
struct vmcb_save_area *save;
struct vmcb_save_area_cached save_cached;
struct vmcb_ctrl_area_cached ctl_cached;
bool use_separate_l2_pat;
unsigned long cr0;
int ret;
@ -2004,6 +2008,17 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
!nested_vmcb_check_save(vcpu, &save_cached, false))
goto out_free;
/*
* Validate gPAT when the shared PAT quirk is disabled (i.e. L2
* has its own gPAT). This is done separately from the
* vmcb_save_area_cached validation above, because gPAT is L2
* state, but the vmcb_save_area_cached is populated with L1 state.
*/
use_separate_l2_pat = (ctl_cached.misc_ctl & SVM_MISC_ENABLE_NP) &&
!kvm_check_has_quirk(vcpu->kvm,
KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT);
if (use_separate_l2_pat && !kvm_pat_valid(kvm_state->hdr.svm.gpat))
goto out_free;
/*
* All checks done, we can enter guest mode. Userspace provides
@ -2030,6 +2045,10 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
nested_copy_vmcb_control_to_cache(svm, ctl);
svm_switch_vmcb(svm, &svm->nested.vmcb02);
if (use_separate_l2_pat)
vmcb_set_gpat(svm->vmcb, kvm_state->hdr.svm.gpat);
nested_vmcb02_prepare_control(svm);
/*