Define a quirk to control whether nested SVM shares L1's PAT with L2 (legacy behavior) or gives L2 its own independent gPAT (correct behavior per the APM).
When the quirk is enabled (default), L2 shares L1's PAT, preserving the legacy KVM behavior. When userspace disables the quirk, KVM correctly virtualizes the PAT for nested SVM guests, giving L2 a separate gPAT as specified in the AMD architecture. Signed-off-by: Jim Mattson <[email protected]> --- Documentation/virt/kvm/api.rst | 14 ++++++++++++++ arch/x86/include/asm/kvm_host.h | 3 ++- arch/x86/include/uapi/asm/kvm.h | 1 + arch/x86/kvm/svm/svm.h | 7 +++++++ 4 files changed, 24 insertions(+), 1 deletion(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 032516783e96..2d56f17e3760 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8551,6 +8551,20 @@ KVM_X86_QUIRK_VMCS12_ALLOW_FREEZE_IN_SMM By default, KVM relaxes the consisten bit to be cleared. Note that the vmcs02 bit is still completely controlled by the host, regardless of the quirk setting. + +KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT By default, KVM for nested SVM guests + shares the IA32_PAT MSR between L1 and + L2. This is legacy behavior and does + not match the AMD architecture + specification. When this quirk is + disabled and nested paging (NPT) is + enabled for L2, KVM correctly + virtualizes a separate guest PAT + register for L2, using the g_pat + field in the VMCB. When NPT is + disabled for L2, L1 and L2 continue + to share the IA32_PAT MSR regardless + of the quirk setting. ======================================== ================================================ 7.32 KVM_CAP_MAX_VCPU_ID diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index d3bdc9828133..0809d8f28208 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -2511,7 +2511,8 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages); KVM_X86_QUIRK_SLOT_ZAP_ALL | \ KVM_X86_QUIRK_STUFF_FEATURE_MSRS | \ KVM_X86_QUIRK_IGNORE_GUEST_PAT | \ - KVM_X86_QUIRK_VMCS12_ALLOW_FREEZE_IN_SMM) + KVM_X86_QUIRK_VMCS12_ALLOW_FREEZE_IN_SMM \ + KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT) #define KVM_X86_CONDITIONAL_QUIRKS \ (KVM_X86_QUIRK_CD_NW_CLEARED | \ diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h index 5f2b30d0405c..3ada2fa9ca86 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -477,6 +477,7 @@ struct kvm_sync_regs { #define KVM_X86_QUIRK_STUFF_FEATURE_MSRS (1 << 8) #define KVM_X86_QUIRK_IGNORE_GUEST_PAT (1 << 9) #define KVM_X86_QUIRK_VMCS12_ALLOW_FREEZE_IN_SMM (1 << 10) +#define KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT (1 << 11) #define KVM_STATE_NESTED_FORMAT_VMX 0 #define KVM_STATE_NESTED_FORMAT_SVM 1 diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index ff1e4b4dc998..67aa5d34332e 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -616,6 +616,13 @@ static inline bool nested_npt_enabled(struct vcpu_svm *svm) return svm->nested.ctl.misc_ctl & SVM_MISC_ENABLE_NP; } +static inline bool l2_has_separate_pat(struct vcpu_svm *svm) +{ + return nested_npt_enabled(svm) && + !kvm_check_has_quirk(svm->vcpu.kvm, + KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT); +} + static inline bool nested_vnmi_enabled(struct vcpu_svm *svm) { return guest_cpu_cap_has(&svm->vcpu, X86_FEATURE_VNMI) && -- 2.53.0.1018.g2bb0e51243-goog
