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

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: cc440cdad5b7 ("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>

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 6fa731464aa214cb8667ac72eeed66fb87d1bce1..adfb04bbf3db9780c0580cddac5aa5977ff8bf21 100644 (file)
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -4967,6 +4967,7 @@ Errors:
 
   struct kvm_svm_nested_state_hdr {
        __u64 vmcb_pa;
+       __u64 gpat;
   };
 
   struct kvm_vmx_nested_state_data {

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 3ada2fa9ca865789c9a99daa028b58e56b2b3e0c..1585ec8040666e503e8f5ad96ac7932fc195332c 100644 (file)
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -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 */

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 1db821181f43f3ea036e81932234716ad81f2578..b326420ac8830ec9b7cefc96b5e6fd6bd5ca92ec 100644 (file)
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -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);
 
        /*