KVM: x86: Snapshot if a vCPU's vendor model is AMD vs. Intel compatible

commit fd706c9b1674e2858766bfbf7430534c2b26fbef upstream.

Add kvm_vcpu_arch.is_amd_compatible to cache if a vCPU's vendor model is
compatible with AMD, i.e. if the vCPU vendor is AMD or Hygon, along with
helpers to check if a vCPU is compatible AMD vs. Intel.  To handle Intel
vs. AMD behavior related to masking the LVTPC entry, KVM will need to
check for vendor compatibility on every PMI injection, i.e. querying for
AMD will soon be a moderately hot path.

Note!  This subtly (or maybe not-so-subtly) makes "Intel compatible" KVM's
default behavior, both if userspace omits (or never sets) CPUID 0x0 and if
userspace sets a completely unknown vendor.  One could argue that KVM
should treat such vCPUs as not being compatible with Intel *or* AMD, but
that would add useless complexity to KVM.

KVM needs to do *something* in the face of vendor specific behavior, and
so unless KVM conjured up a magic third option, choosing to treat unknown
vendors as neither Intel nor AMD means that checks on AMD compatibility
would yield Intel behavior, and checks for Intel compatibility would yield
AMD behavior.  And that's far worse as it would effectively yield random
behavior depending on whether KVM checked for AMD vs. Intel vs. !AMD vs.
!Intel.  And practically speaking, all x86 CPUs follow either Intel or AMD
architecture, i.e. "supporting" an unknown third architecture adds no
value.

Deliberately don't convert any of the existing guest_cpuid_is_intel()
checks, as the Intel side of things is messier due to some flows explicitly
checking for exactly vendor==Intel, versus some flows assuming anything
that isn't "AMD compatible" gets Intel behavior.  The Intel code will be
cleaned up in the future.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240405235603.1173076-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index fb9f5fa96cc964d39041e2757773a21754dffc2c..ccba66da7a5d76d85a724fa7f4d641a930b2158e 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -828,6 +828,7 @@ struct kvm_vcpu_arch {
        int cpuid_nent;
        struct kvm_cpuid_entry2 *cpuid_entries;
        struct kvm_hypervisor_cpuid kvm_cpuid;
+       bool is_amd_compatible;
 
        /*
         * FIXME: Drop this macro and use KVM_NR_GOVERNED_FEATURES directly

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d65f91d0a8bca3bd156da45029a6975fea487c59..77458137cab179411259be6a80730b51cfbf37cd 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -362,6 +362,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
        kvm_update_pv_runtime(vcpu);
 
+       vcpu->arch.is_amd_compatible = guest_cpuid_is_amd_or_hygon(vcpu);
        vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
        vcpu->arch.reserved_gpa_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu);
 

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 284fa4704553da1345731927225084e7daeeba4b..57ee789ada1411eef3262d67926944ea7f8f2326 100644 (file)
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -125,6 +125,16 @@ static inline bool guest_cpuid_is_intel(struct kvm_vcpu *vcpu)
        return best && is_guest_vendor_intel(best->ebx, best->ecx, best->edx);
 }
 
+static inline bool guest_cpuid_is_amd_compatible(struct kvm_vcpu *vcpu)
+{
+       return vcpu->arch.is_amd_compatible;
+}
+
+static inline bool guest_cpuid_is_intel_compatible(struct kvm_vcpu *vcpu)
+{
+       return !guest_cpuid_is_amd_compatible(vcpu);
+}
+
 static inline int guest_cpuid_family(struct kvm_vcpu *vcpu)
 {
        struct kvm_cpuid_entry2 *best;

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 11c484d72eab2f97256a7afa33fd461db6ec2334..294775b7383b42d0340be6f10cd04ab6432a55d6 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4788,7 +4788,7 @@ static void reset_guest_rsvds_bits_mask(struct kvm_vcpu *vcpu,
                                context->cpu_role.base.level, is_efer_nx(context),
                                guest_can_use(vcpu, X86_FEATURE_GBPAGES),
                                is_cr4_pse(context),
-                               guest_cpuid_is_amd_or_hygon(vcpu));
+                               guest_cpuid_is_amd_compatible(vcpu));
 }
 
 static void __reset_rsvds_bits_mask_ept(struct rsvd_bits_validate *rsvd_check,

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4ed8a7dc05369e3750189159672a3d02305fd100..cab7680f0d68114e617c91bc880dc36da33b3c46 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3317,7 +3317,7 @@ static bool is_mci_status_msr(u32 msr)
 static bool can_set_mci_status(struct kvm_vcpu *vcpu)
 {
        /* McStatusWrEn enabled? */
-       if (guest_cpuid_is_amd_or_hygon(vcpu))
+       if (guest_cpuid_is_amd_compatible(vcpu))
                return !!(vcpu->arch.msr_hwcr & BIT_ULL(18));
 
        return false;