[RFC PATCH v2 02/11] KVM: x86: Advertise CPUID.7.2.EDX and RRSBA_CTRL support

[Chao Gao]

From: Zhang Chen <chen.zhang@xxxxxxxxx>

Add a kvm-only CPUID feature leaf for CPUID.7.2.EDX and RRSBA_CTRL
as the first feature in the leaf.

RRSBA_CTRL is enumerated by CPUID.7.2.EDX[2]. If supported, RRSBA_DIS_U
(bit 5) and RRSBA_DIS_S (bit 6) of IA32_SPEC_CTRL MSR can be used to
disable RRSBA behavior for CPL3 and CPL0/1/2 respectively.

Note that KVM does not intercept guests' IA32_SPEC_CTRL MSR accesses
after a non-zero is written to the MSR. Therefore, guests can already
toggle the two bits if the host supports RRSBA_CTRL, and no extra code
is needed to allow guests to toggle the two bits.

Signed-off-by: Zhang Chen <chen.zhang@xxxxxxxxx>
Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
Tested-by: Jiaan Lu <jiaan.lu@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c         | 22 +++++++++++++++++++---
 arch/x86/kvm/reverse_cpuid.h |  7 +++++++
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9583a110cf5f..f024c3ac2203 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -685,6 +685,10 @@ void kvm_set_cpu_caps(void)
 		SF(SGX1) | SF(SGX2) | SF(SGX_EDECCSSA)
 	);
 
+	kvm_cpu_cap_init_kvm_defined(CPUID_7_2_EDX,
+		SF(RRSBA_CTRL)
+	);
+
 	kvm_cpu_cap_mask(CPUID_8000_0001_ECX,
 		F(LAHF_LM) | F(CMP_LEGACY) | 0 /*SVM*/ | 0 /* ExtApicSpace */ |
 		F(CR8_LEGACY) | F(ABM) | F(SSE4A) | F(MISALIGNSSE) |
@@ -949,13 +953,14 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		break;
 	/* function 7 has additional index. */
 	case 7:
-		entry->eax = min(entry->eax, 1u);
+		entry->eax = min(entry->eax, 2u);
 		cpuid_entry_override(entry, CPUID_7_0_EBX);
 		cpuid_entry_override(entry, CPUID_7_ECX);
 		cpuid_entry_override(entry, CPUID_7_EDX);
 
-		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
-		if (entry->eax == 1) {
+		max_idx = entry->eax;
+
+		if (max_idx >= 1) {
 			entry = do_host_cpuid(array, function, 1);
 			if (!entry)
 				goto out;
@@ -965,6 +970,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			entry->ebx = 0;
 			entry->ecx = 0;
 		}
+
+		if (max_idx >= 2) {
+			entry = do_host_cpuid(array, function, 2);
+			if (!entry)
+				goto out;
+
+			cpuid_entry_override(entry, CPUID_7_2_EDX);
+			entry->eax = 0;
+			entry->ebx = 0;
+			entry->ecx = 0;
+		}
 		break;
 	case 0xa: { /* Architectural Performance Monitoring */
 		union cpuid10_eax eax;
diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
index a5717282bb9c..72bad8314a9c 100644
--- a/arch/x86/kvm/reverse_cpuid.h
+++ b/arch/x86/kvm/reverse_cpuid.h
@@ -15,6 +15,7 @@ enum kvm_only_cpuid_leafs {
 	CPUID_12_EAX	 = NCAPINTS,
 	CPUID_7_1_EDX,
 	CPUID_8000_0007_EDX,
+	CPUID_7_2_EDX,
 	NR_KVM_CPU_CAPS,
 
 	NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
@@ -47,6 +48,9 @@ enum kvm_only_cpuid_leafs {
 /* CPUID level 0x80000007 (EDX). */
 #define KVM_X86_FEATURE_CONSTANT_TSC	KVM_X86_FEATURE(CPUID_8000_0007_EDX, 8)
 
+/* Intel-defined sub-features, CPUID level 0x00000007:2 (EDX) */
+#define KVM_X86_FEATURE_RRSBA_CTRL	KVM_X86_FEATURE(CPUID_7_2_EDX, 2)
+
 struct cpuid_reg {
 	u32 function;
 	u32 index;
@@ -69,6 +73,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
 	[CPUID_8000_0007_EBX] = {0x80000007, 0, CPUID_EBX},
 	[CPUID_7_EDX]         = {         7, 0, CPUID_EDX},
 	[CPUID_7_1_EAX]       = {         7, 1, CPUID_EAX},
+	[CPUID_7_2_EDX]       = {         7, 2, CPUID_EDX},
 	[CPUID_12_EAX]        = {0x00000012, 0, CPUID_EAX},
 	[CPUID_8000_001F_EAX] = {0x8000001f, 0, CPUID_EAX},
 	[CPUID_7_1_EDX]       = {         7, 1, CPUID_EDX},
@@ -108,6 +113,8 @@ static __always_inline u32 __feature_translate(int x86_feature)
 		return KVM_X86_FEATURE_SGX_EDECCSSA;
 	else if (x86_feature == X86_FEATURE_CONSTANT_TSC)
 		return KVM_X86_FEATURE_CONSTANT_TSC;
+	else if (x86_feature == X86_FEATURE_RRSBA_CTRL)
+		return KVM_X86_FEATURE_RRSBA_CTRL;
 
 	return x86_feature;
 }
-- 
2.40.0