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KVM: x86: Make sure KVM_CPUID_FEATURES really are KVM_CPUID_FEATURES

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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>
This commit is contained in:
Paul Durrant 2021-11-05 09:51:01 +00:00 committed by Paolo Bonzini
parent 8b44b174f6
commit 760849b147
5 changed files with 47 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/kvm_host.h
View File

@ -725,6 +725,7 @@ struct kvm_vcpu_arch {
int cpuid_nent;
struct kvm_cpuid_entry2 *cpuid_entries;
u32 kvm_cpuid_base;
u64 reserved_gpa_bits;
int maxphyaddr;

5
arch/x86/include/asm/processor.h
View File

@ -807,11 +807,14 @@ static inline u32 amd_get_nodes_per_socket(void) { return 0; }
static inline u32 amd_get_highest_perf(void) { return 0; }
#endif
#define for_each_possible_hypervisor_cpuid_base(function) \
for (function = 0x40000000; function < 0x40010000; function += 0x100)
static inline uint32_t hypervisor_cpuid_base(const char *sig, uint32_t leaves)
{
uint32_t base, eax, signature[3];
for (base = 0x40000000; base < 0x40010000; base += 0x100) {
for_each_possible_hypervisor_cpuid_base(base) {
cpuid(base, &eax, &signature[0], &signature[1], &signature[2]);
if (!memcmp(sig, signature, 12) &&

1
arch/x86/include/uapi/asm/kvm_para.h
View File

@ -8,6 +8,7 @@
* should be used to determine that a VM is running under KVM.
*/
#define KVM_CPUID_SIGNATURE 0x40000000
#define KVM_SIGNATURE "KVMKVMKVM\0\0\0"
/* This CPUID returns two feature bitmaps in eax, edx. Before enabling
* a particular paravirtualization, the appropriate feature bit should

2
arch/x86/kernel/kvm.c
View File

@ -755,7 +755,7 @@ static noinline uint32_t __kvm_cpuid_base(void)
return 0; /* So we don't blow up on old processors */
if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);
return hypervisor_cpuid_base(KVM_SIGNATURE, 0);
return 0;
}

46
arch/x86/kvm/cpuid.c
View File

@ -99,11 +99,45 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
return 0;
}
static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
{
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);
}
void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;
best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
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];