[RFC PATCH 10/73] KVM: x86: Introduce vendor feature to expose vendor-specific CPUID

Lai Jiangshan
2024-02-26T14:35:10Z

For the PVM guest, it needs to detect PVM support early, even before IDT
setup, so the cpuid instruction is used. Moreover, in order to
differentiate PVM from VMX/SVM, a new CPUID is introduced to expose
vendor-specific features. Currently, only PVM uses it.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/include/uapi/asm/kvm_para.h | 8 +++++++-
arch/x86/kvm/cpuid.c | 26 +++++++++++++++++++++++++-
arch/x86/kvm/cpuid.h | 3 +++
3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 6e64b27b2c1e..f999f1d32423 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -5,7 +5,9 @@
#include <linux/types.h>

/* This CPUID returns the signature 'KVMKVMKVM' in ebx, ecx, and edx. It
- * should be used to determine that a VM is running under KVM.
+ * should be used to determine that a VM is running under KVM. And it
+ * returns KVM_CPUID_FEATURES in eax if vendor feature is not enabled,
+ * otherwise KVM_CPUID_VENDOR_FEATURES.
*/
#define KVM_CPUID_SIGNATURE 0x40000000
#define KVM_SIGNATURE "KVMKVMKVM\0\0\0"
@@ -16,6 +18,10 @@
* in edx.
*/
#define KVM_CPUID_FEATURES 0x40000001
+/* This CPUID returns the vendor feature bitmaps in eax and the vendor
+ * signature in ebx.
+ */
+#define KVM_CPUID_VENDOR_FEATURES 0x40000002
#define KVM_FEATURE_CLOCKSOURCE 0
#define KVM_FEATURE_NOP_IO_DELAY 1
#define KVM_FEATURE_MMU_OP 2
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index dda6fc4cfae8..31ae843a6180 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -36,6 +36,16 @@
u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly;
EXPORT_SYMBOL_GPL(kvm_cpu_caps);

+u32 kvm_cpuid_vendor_features;
+EXPORT_SYMBOL_GPL(kvm_cpuid_vendor_features);
+u32 kvm_cpuid_vendor_signature;
+EXPORT_SYMBOL_GPL(kvm_cpuid_vendor_signature);
+
+static inline bool has_kvm_cpuid_vendor_features(void)
+{
+ return !!kvm_cpuid_vendor_signature;
+}
+
u32 xstate_required_size(u64 xstate_bv, bool compacted)
{
int feature_bit = 0;
@@ -1132,7 +1142,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
break;
case KVM_CPUID_SIGNATURE: {
const u32 *sigptr = (const u32 *)KVM_SIGNATURE;
- entry->eax = KVM_CPUID_FEATURES;
+ if (!has_kvm_cpuid_vendor_features())
+ entry->eax = KVM_CPUID_FEATURES;
+ else
+ entry->eax = KVM_CPUID_VENDOR_FEATURES;
entry->ebx = sigptr[0];
entry->ecx = sigptr[1];
entry->edx = sigptr[2];
@@ -1160,6 +1173,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
entry->ecx = 0;
entry->edx = 0;
break;
+ case KVM_CPUID_VENDOR_FEATURES:
+ if (!has_kvm_cpuid_vendor_features()) {
+ entry->eax = 0;
+ entry->ebx = 0;
+ } else {
+ entry->eax = kvm_cpuid_vendor_features;
+ entry->ebx = kvm_cpuid_vendor_signature;
+ }
+ entry->ecx = 0;
+ entry->edx = 0;
+ break;
case 0x80000000:
entry->eax = min(entry->eax, 0x80000022);
/*
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 0b90532b6e26..b93e5fec4808 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -8,6 +8,9 @@
#include <asm/processor.h>
#include <uapi/asm/kvm_para.h>

+extern u32 kvm_cpuid_vendor_features;
+extern u32 kvm_cpuid_vendor_signature;
+
extern u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly;
void kvm_set_cpu_caps(void);

--
2.19.1.6.gb485710b