KVM: x86: Make sure KVM_CPUID_FEATURES really are KVM_CPUID_FEATURES

Currently when kvm_update_cpuid_runtime() runs, it assumes that the
KVM_CPUID_FEATURES leaf is located at 0x40000001. This is not true,
however, if Hyper-V support is enabled. In this case the KVM leaves will
be offset.

This patch introdues as new 'kvm_cpuid_base' field into struct
kvm_vcpu_arch to track the location of the KVM leaves and function
kvm_update_kvm_cpuid_base() (called from kvm_set_cpuid()) to locate the
leaves using the 'KVMKVMKVM\0\0\0' signature (which is now given a
definition in kvm_para.h). Adjustment of KVM_CPUID_FEATURES will hence now
target the correct leaf.

NOTE: A new for_each_possible_hypervisor_cpuid_base() macro is intoduced
      into processor.h to avoid having duplicate code for the iteration
      over possible hypervisor base leaves.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Message-Id: <20211105095101.5384-3-pdurrant@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 40 insertions, 6 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 41529c168e91..e19dabf1848b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -99,11 +99,45 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
 	return 0;
 }
 
-void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
+static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
 {
-	struct kvm_cpuid_entry2 *best;
+	u32 function;
+	struct kvm_cpuid_entry2 *entry;
+
+	vcpu->arch.kvm_cpuid_base = 0;
+
+	for_each_possible_hypervisor_cpuid_base(function) {
+		entry = kvm_find_cpuid_entry(vcpu, function, 0);
+
+		if (entry) {
+			u32 signature[3];
+
+			signature[0] = entry->ebx;
+			signature[1] = entry->ecx;
+			signature[2] = entry->edx;
+
+			BUILD_BUG_ON(sizeof(signature) > sizeof(KVM_SIGNATURE));
+			if (!memcmp(signature, KVM_SIGNATURE, sizeof(signature))) {
+				vcpu->arch.kvm_cpuid_base = function;
+				break;
+			}
+		}
+	}
+}
+
+struct kvm_cpuid_entry2 *kvm_find_kvm_cpuid_features(struct kvm_vcpu *vcpu)
+{
+	u32 base = vcpu->arch.kvm_cpuid_base;
+
+	if (!base)
+		return NULL;
+
+	return kvm_find_cpuid_entry(vcpu, base | KVM_CPUID_FEATURES, 0);
+}
 
-	best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
+void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best = kvm_find_kvm_cpuid_features(vcpu);
 
 	/*
 	 * save the feature bitmap to avoid cpuid lookup for every PV
@@ -142,7 +176,7 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
 		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
 		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
 
-	best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
+	best = kvm_find_kvm_cpuid_features(vcpu);
 	if (kvm_hlt_in_guest(vcpu->kvm) && best &&
 		(best->eax & (1 << KVM_FEATURE_PV_UNHALT)))
 		best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
@@ -252,6 +286,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
     vcpu->arch.cpuid_entries = e2;
     vcpu->arch.cpuid_nent = nent;
 
+    kvm_update_kvm_cpuid_base(vcpu);
     kvm_update_cpuid_runtime(vcpu);
     kvm_vcpu_after_set_cpuid(vcpu);
 
@@ -872,8 +907,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		}
 		break;
 	case KVM_CPUID_SIGNATURE: {
-		static const char signature[12] = "KVMKVMKVM\0\0";
-		const u32 *sigptr = (const u32 *)signature;
+		const u32 *sigptr = (const u32 *)KVM_SIGNATURE;
 		entry->eax = KVM_CPUID_FEATURES;
 		entry->ebx = sigptr[0];
 		entry->ecx = sigptr[1];