[PATCH v2] KVM: x86: Add Intel CPUID.1F cpuid emulation support

[Like Xu <like.xu@linux.intel.com>]

Some new systems have multiple software-visible die within each package.
Add support to expose Intel V2 Extended Topology Enumeration Leaf CPUID.1F.

Co-developed-by: Xiaoyao Li <xiaoyao.li@linux.intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@linux.intel.com>
Signed-off-by: Like Xu <like.xu@linux.intel.com>
---

==changelog==
v2:
- Apply cpuid.1f check rule on Intel SDM page 3-222 Vol.2A
- Add comment to handle 0x1f anf 0xb in common code
- Reduce check time in a descending-break style

v1: https://lkml.org/lkml/2019/4/22/28

 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 fd39516..f9b529e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -425,6 +425,11 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	switch (function) {
 	case 0:
+		/* Check if the cpuid leaf 0x1f is actually implemented */
+		if (entry->eax >= 0x1f && (cpuid_ebx(0x1f) & 0x0000ffff)) {
+			entry->eax = 0x1f;
+			break;
+		}
 		entry->eax = min(entry->eax, (u32)(f_intel_pt ? 0x14 : 0xd));
 		break;
 	case 1:
@@ -544,7 +549,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		entry->edx = edx.full;
 		break;
 	}
-	/* function 0xb has additional index. */
+	/*
+	 * Intel documentation states that 0x1f and 0xb have
+	 * identical formats and thus can be handled by common code.
+	 * (Intel SDM Vol. 2A - Instruction Set Reference - CPUID)
+	 */
+	case 0x1f:
 	case 0xb: {
 		int i, level_type;
 
-- 
1.8.3.1