[PATCH] KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT

[Jim Mattson <jmattson@google.com>]

When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled and the vCPU is in
guest mode with nested NPT enabled, guest accesses to IA32_PAT are
redirected to the gPAT register, which is stored in VMCB02's g_pat field.

Non-guest accesses (e.g. from userspace) to IA32_PAT are always redirected
to hPAT, which is stored in vcpu->arch.pat.

Directing host-initiated accesses to hPAT ensures that KVM_GET/SET_MSRS and
KVM_GET/SET_NESTED_STATE are independent of each other and can be ordered
arbitrarily during save and restore. gPAT is saved and restored separately
via KVM_GET/SET_NESTED_STATE.

Use WARN_ON_ONCE to flag any host-initiated accesses originating from KVM
itself rather than userspace.

Use pr_warn_once to flag any use of the common MSR-handling code (now
shared by VMX and TDX) for IA32_PAT by a vCPU that is SVM-capable.

Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
Signed-off-by: Jim Mattson <jmattson@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/nested.c |  9 ---------
 arch/x86/kvm/svm/svm.c    | 36 +++++++++++++++++++++++++++++++++---
 arch/x86/kvm/svm/svm.h    |  1 -
 3 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 58574e803812..8c9dd685b616 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -703,15 +703,6 @@ static int nested_svm_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3,
 	return 0;
 }
 
-void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm)
-{
-	if (!svm->nested.vmcb02.ptr)
-		return;
-
-	/* FIXME: merge g_pat from vmcb01 and vmcb12.  */
-	vmcb_set_gpat(svm->nested.vmcb02.ptr, svm->vmcb01.ptr->save.g_pat);
-}
-
 static bool nested_vmcb12_has_lbrv(struct kvm_vcpu *vcpu)
 {
 	return guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 56b6bd5dfdca..8d968ead6f45 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2767,6 +2767,20 @@ static bool sev_es_prevent_msr_access(struct kvm_vcpu *vcpu,
 	       !msr_write_intercepted(vcpu, msr_info->index);
 }
 
+static bool svm_pat_accesses_gpat(struct kvm_vcpu *vcpu, bool from_host)
+{
+	/*
+	 * When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled and nested
+	 * NPT is enabled, L2 has a separate PAT from L1.  Guest accesses
+	 * to IA32_PAT while running L2 target L2's gPAT; host-initiated
+	 * accesses always target L1's hPAT so that KVM_GET/SET_MSRS and
+	 * KVM_GET/SET_NESTED_STATE are independent of each other and can
+	 * be ordered arbitrarily during save and restore.
+	 */
+	WARN_ON_ONCE(from_host && vcpu->wants_to_run);
+	return !from_host && is_guest_mode(vcpu) && l2_has_separate_pat(vcpu);
+}
+
 static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -2883,6 +2897,12 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_AMD64_DE_CFG:
 		msr_info->data = svm->msr_decfg;
 		break;
+	case MSR_IA32_CR_PAT:
+		if (svm_pat_accesses_gpat(vcpu, msr_info->host_initiated)) {
+			msr_info->data = svm->vmcb->save.g_pat;
+			break;
+		}
+		return kvm_get_msr_common(vcpu, msr_info);
 	default:
 		return kvm_get_msr_common(vcpu, msr_info);
 	}
@@ -2966,13 +2986,23 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 
 		break;
 	case MSR_IA32_CR_PAT:
+		if (svm_pat_accesses_gpat(vcpu, msr->host_initiated)) {
+			if (!kvm_pat_valid(data))
+				return 1;
+
+			vmcb_set_gpat(svm->vmcb, data);
+			break;
+		}
+
 		ret = kvm_set_msr_common(vcpu, msr);
 		if (ret)
 			break;
 
-		vmcb_set_gpat(svm->vmcb01.ptr, data);
-		if (is_guest_mode(vcpu))
-			nested_vmcb02_compute_g_pat(svm);
+		if (npt_enabled) {
+			vmcb_set_gpat(svm->vmcb01.ptr, data);
+			if (is_guest_mode(vcpu) && !l2_has_separate_pat(vcpu))
+				vmcb_set_gpat(svm->vmcb, data);
+		}
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr->host_initiated &&
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index fdd6286d965e..677e899bda33 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -881,7 +881,6 @@ void nested_copy_vmcb_control_to_cache(struct vcpu_svm *svm,
 void nested_copy_vmcb_save_to_cache(struct vcpu_svm *svm,
 				    struct vmcb_save_area *save);
 void nested_sync_control_from_vmcb02(struct vcpu_svm *svm);
-void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm);
 void svm_switch_vmcb(struct vcpu_svm *svm, struct kvm_vmcb_info *target_vmcb);
 
 extern struct kvm_x86_nested_ops svm_nested_ops;
-- 
2.53.0.1213.gd9a14994de-goog