[PATCH v4] KVM: x86: Add Intel CPUID.1F cpuid emulation support

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

Add support to expose Intel V2 Extended Topology Enumeration Leaf for
some new systems with multiple software-visible die within each package.

Because unimplemented and unexposed leaves should be explicitly reported
as zero, there is no need to limit cpuid.0.eax to the maximum value of
feature configuration but limit it to the highest leaf implemented in
the current code. A single clamping seems sufficient and cheaper.

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==

v4:
- Limited cpuid.0.eax to the highest leaf implemented in KVM

v3: https://lkml.org/lkml/2019/5/26/64
- Refine commit message and comment

v2: https://lkml.org/lkml/2019/4/25/1246

- 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 | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e18a9f9f65b5..f819011e6a13 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -426,7 +426,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	switch (function) {
 	case 0:
-		entry->eax = min(entry->eax, (u32)(f_intel_pt ? 0x14 : 0xd));
+		/* Limited to the highest leaf implemented in KVM. */
+		entry->eax = min(entry->eax, 0x1f);
 		break;
 	case 1:
 		entry->edx &= kvm_cpuid_1_edx_x86_features;
@@ -546,7 +547,11 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		entry->edx = edx.full;
 		break;
 	}
-	/* function 0xb has additional index. */
+	/*
+	 * Per Intel's SDM, the 0x1f is a superset of 0xb,
+	 * thus they can be handled by common code.
+	 */
+	case 0x1f:
 	case 0xb: {
 		int i, level_type;
 
-- 
2.21.0