[PATCH v2 2/2] x86/Intel: use CPUID bit to determine PPIN availability

[Jan Beulich <jbeulich@xxxxxxxx>]

As of SDM revision 076 there is a CPUID bit for this functionality. Use
it to amend the existing model-based logic.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
It continues to be unclear for which CPU models, if any, the PPIN_CAP
bit in PLATFORM_INFO could be used in favor of a model check.
---
v2: Don't rename AMD's identifier in xen-cpuid.c. Name Intel's just
    "ppin" as well. Move str_7b1[]. Update a comment.

--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -195,6 +195,11 @@ static const char *const str_e21a[32] =
     [ 6] = "nscb",
 };
 
+static const char *const str_7b1[32] =
+{
+    [ 0] = "ppin",
+};
+
 static const struct {
     const char *name;
     const char *abbr;
@@ -213,6 +218,7 @@ static const struct {
     { "0x00000007:0.edx", "7d0", str_7d0 },
     { "0x00000007:1.eax", "7a1", str_7a1 },
     { "0x80000021.eax",  "e21a", str_e21a },
+    { "0x00000007:1.ebx", "7b1", str_7b1 },
 };
 
 #define COL_ALIGN "18"
--- a/xen/arch/x86/cpu/mcheck/mce_intel.c
+++ b/xen/arch/x86/cpu/mcheck/mce_intel.c
@@ -859,12 +859,20 @@ static void intel_init_ppin(const struct
     /*
      * Even if testing the presence of the MSR would be enough, we don't
      * want to risk the situation where other models reuse this MSR for
-     * other purposes.
+     * other purposes.  Despite the late addition of a CPUID bit (rendering
+     * the MSR architectural), keep using the same detection logic there.
      */
     switch ( c->x86_model )
     {
         uint64_t val;
 
+    default:
+        if ( !cpu_has(c, X86_FEATURE_INTEL_PPIN) )
+        {
+            ppin_msr = 0;
+            return;
+        }
+        fallthrough;
     case 0x3e: /* IvyBridge X */
     case 0x3f: /* Haswell X */
     case 0x4f: /* Broadwell X */
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -299,6 +299,9 @@ XEN_CPUFEATURE(FSRCS,        10*32+12) /
 XEN_CPUFEATURE(LFENCE_DISPATCH,    11*32+ 2) /*A  LFENCE always serializing */
 XEN_CPUFEATURE(NSCB,               11*32+ 6) /*A  Null Selector Clears Base 
(and limit too) */
 
+/* Intel-defined CPU features, CPUID level 0x00000007:1.ebx, word 12 */
+XEN_CPUFEATURE(INTEL_PPIN,         12*32+ 0) /*   Protected Processor 
Inventory Number */
+
 #endif /* XEN_CPUFEATURE */
 
 /* Clean up from a default include.  Close the enum (for C). */
--- a/xen/include/xen/lib/x86/cpuid.h
+++ b/xen/include/xen/lib/x86/cpuid.h
@@ -16,6 +16,7 @@
 #define FEATURESET_7d0    9 /* 0x00000007:0.edx    */
 #define FEATURESET_7a1   10 /* 0x00000007:1.eax    */
 #define FEATURESET_e21a  11 /* 0x80000021.eax      */
+#define FEATURESET_7b1   12 /* 0x00000007:1.ebx    */
 
 struct cpuid_leaf
 {
@@ -188,6 +189,10 @@ struct cpuid_policy
                 uint32_t _7a1;
                 struct { DECL_BITFIELD(7a1); };
             };
+            union {
+                uint32_t _7b1;
+                struct { DECL_BITFIELD(7b1); };
+            };
         };
     } feat;