Use the respective ARCH_CAPABILITIES MSR bit, but don't expose the MSR
to guests yet.

Signed-off-by: Jan Beulich <jbeul...@suse.com>
Tested-by: Juergen Gross <jgr...@suse.com>
Reviewed-by: Juergen Gross <jgr...@suse.com>
---
v3: Re-base.
v2: New.

--- a/tools/libxl/libxl_cpuid.c
+++ b/tools/libxl/libxl_cpuid.c
@@ -204,6 +204,7 @@ int libxl_cpuid_parse_config(libxl_cpuid
         {"avx512-4fmaps",0x00000007,  0, CPUID_REG_EDX,  3,  1},
         {"ibrsb",        0x00000007,  0, CPUID_REG_EDX, 26,  1},
         {"stibp",        0x00000007,  0, CPUID_REG_EDX, 27,  1},
+        {"arch-caps",    0x00000007,  0, CPUID_REG_EDX, 29,  1},
 
         {"lahfsahf",     0x80000001, NA, CPUID_REG_ECX,  0,  1},
         {"cmplegacy",    0x80000001, NA, CPUID_REG_ECX,  1,  1},
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -143,6 +143,7 @@ static const char *str_7d0[32] =
     [ 2] = "avx512_4vnniw", [ 3] = "avx512_4fmaps",
 
     [26] = "ibrsb",         [27] = "stibp",
+    /* 28 */                [29] = "arch_caps",
 };
 
 static struct {
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1545,7 +1545,16 @@ void __init noreturn __start_xen(unsigne
     cr4_pv32_mask = mmu_cr4_features & XEN_CR4_PV32_BITS;
 
     if ( opt_xpti < 0 )
-        opt_xpti = boot_cpu_data.x86_vendor != X86_VENDOR_AMD;
+    {
+        uint64_t caps = 0;
+
+        if ( boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
+            caps = ARCH_CAPABILITIES_RDCL_NO;
+        else if ( boot_cpu_has(X86_FEATURE_ARCH_CAPS) )
+            rdmsrl(MSR_ARCH_CAPABILITIES, caps);
+
+        opt_xpti = !(caps & ARCH_CAPABILITIES_RDCL_NO);
+    }
     if ( opt_xpti )
         setup_clear_cpu_cap(X86_FEATURE_NO_XPTI);
     else
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -40,6 +40,8 @@
 #define PRED_CMD_IBPB                  (_AC(1, ULL) << 0)
 
 #define MSR_ARCH_CAPABILITIES          0x0000010a
+#define ARCH_CAPABILITIES_RDCL_NO      (_AC(1, ULL) << 0)
+#define ARCH_CAPABILITIES_IBRS_ALL     (_AC(1, ULL) << 1)
 
 /* Intel MSRs. Some also available on other CPUs */
 #define MSR_IA32_PERFCTR0              0x000000c1
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -244,6 +244,7 @@ XEN_CPUFEATURE(AVX512_4VNNIW, 9*32+ 2) /
 XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A  AVX512 Multiply Accumulation 
Single Precision */
 XEN_CPUFEATURE(IBRSB,         9*32+26) /*A  IBRS and IBPB support (used by 
Intel) */
 XEN_CPUFEATURE(STIBP,         9*32+27) /*A! STIBP */
+XEN_CPUFEATURE(ARCH_CAPS,     9*32+29) /*   IA32_ARCH_CAPABILITIES MSR */
 
 #endif /* XEN_CPUFEATURE */
 




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