[PATCH v2 2/2] KVM: x86: Expose Predictive Store Forwarding Disable on Intel parts

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Intel enumerates support for PSFD in CPUID.(EAX=7,ECX=2):EDX.PSFD[bit
0]. Report support for this feature in KVM if it is available on the
host.

Presumably, this feature bit, like its AMD counterpart, is not welcome
in cpufeatures.h, so add a local definition of this feature in KVM.

Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 07be45c5bb93..b5af9e451bef 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -62,6 +62,7 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
  * This one is tied to SSB in the user API, and not
  * visible in /proc/cpuinfo.
  */
+#define KVM_X86_FEATURE_PSFD		0          /* Predictive Store Forwarding Disable */
 #define KVM_X86_FEATURE_AMD_PSFD	(13*32+28) /* Predictive Store Forwarding Disable */
 
 #define F feature_bit
@@ -677,9 +678,9 @@ void kvm_set_cpu_caps(void)
 	);
 
 	/*
-	 * AMD has separate bits for each SPEC_CTRL bit.
-	 * arch/x86/kernel/cpu/bugs.c is kind enough to
-	 * record that in cpufeatures so use them.
+	 * AMD has separate bits for each SPEC_CTRL bit.  Except for
+	 * PSFD, arch/x86/kernel/cpu/bugs.c is kind enough to record
+	 * that in cpufeatures so use them.
 	 */
 	if (boot_cpu_has(X86_FEATURE_IBPB))
 		kvm_cpu_cap_set(X86_FEATURE_AMD_IBPB);
@@ -880,13 +881,13 @@ 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);
+		/* KVM only supports leaf 7 indices 0 through 2. */
+		max_idx = 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) {
+		if (max_idx >= 1) {
 			entry = do_host_cpuid(array, function, 1);
 			if (!entry)
 				goto out;
@@ -896,6 +897,16 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			entry->ecx = 0;
 			entry->edx = 0;
 		}
+		if (max_idx >= 2) {
+			entry = do_host_cpuid(array, function, 2);
+			if (!entry)
+				goto out;
+
+			entry->eax = 0;
+			entry->ebx = 0;
+			entry->ecx = 0;
+			entry->edx &= BIT(KVM_X86_FEATURE_PSFD);
+		}
 		break;
 	case 9:
 		break;
-- 
2.37.2.672.g94769d06f0-goog




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