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

Commit Message

Lai Jiangshan Feb. 26, 2024, 2:35 p.m. UTC

From: Lai Jiangshan <[e-mail]>

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 <[e-mail]>
Signed-off-by: Hou Wenlong <[e-mail]>
---
 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(-)

Patch

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);