[PATCH v1] KVM: x86: expose AVX512_BF16 feature to guest

[Jing Liu]

AVX512 BFLOAT16 instructions support 16-bit BFLOAT16 floating-point
format (BF16) for deep learning optimization.

Intel adds AVX512 BFLOAT16 feature in CooperLake, which is CPUID.7.1.EAX[5].

Detailed information of the CPUID bit can be found here,
https://software.intel.com/sites/default/files/managed/c5/15/\
architecture-instruction-set-extensions-programming-reference.pdf.

Signed-off-by: Jing Liu <jing2.liu@xxxxxxxxxxxxxxx>
---

This patch depends on kernel patch https://lkml.org/lkml/2019/6/19/912
and Paolo's patch set https://lkml.org/lkml/2019/7/4/468.

 arch/x86/kvm/cpuid.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8fc6039..0c125dd 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -358,9 +358,13 @@ static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index)
 		F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) |
 		F(MD_CLEAR);
 
+	/* cpuid 7.1.eax */
+	const u32 kvm_cpuid_7_1_eax_x86_features =
+		F(AVX512_BF16);
+
 	switch (index) {
 	case 0:
-		entry->eax = 0;
+		entry->eax = min(entry->eax, 1);
 		entry->ebx &= kvm_cpuid_7_0_ebx_x86_features;
 		cpuid_mask(&entry->ebx, CPUID_7_0_EBX);
 		/* TSC_ADJUST is emulated */
@@ -384,6 +388,12 @@ static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index)
 		 */
 		entry->edx |= F(ARCH_CAPABILITIES);
 		break;
+	case 1:
+		entry->eax &= kvm_cpuid_7_1_eax_x86_features;
+		entry->ebx = 0;
+		entry->ecx = 0;
+		entry->edx = 0;
+		break;
 	default:
 		WARN_ON_ONCE(1);
 		entry->eax = 0;
-- 
1.8.3.1