Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 pti fixes from Thomas Gleixner:
"Two small updates for the speculative distractions:

- Make it more clear to the compiler that array_index_mask_nospec()
is not subject for optimizations. It's not perfect, but ...

- Don't report XEN PV guests as vulnerable because their mitigation
state depends on the hypervisor. Report unknown and refer to the
hypervisor requirement"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/spectre_v1: Disable compiler optimizations over array_index_mask_nospec()
x86/pti: Don't report XenPV as vulnerable

arch/x86/include/asm/barrier.h

···
 {
 	unsigned long mask;
 
-	asm ("cmp %1,%2; sbb %0,%0;"
+	asm volatile ("cmp %1,%2; sbb %0,%0;"
 			:"=r" (mask)
 			:"g"(size),"r" (index)
 			:"cc");

arch/x86/kernel/cpu/bugs.c

···
 #include <asm/pgtable.h>
 #include <asm/set_memory.h>
 #include <asm/intel-family.h>
+#include <asm/hypervisor.h>
 
 static void __init spectre_v2_select_mitigation(void);
 static void __init ssb_select_mitigation(void);
···
 	case X86_BUG_CPU_MELTDOWN:
 		if (boot_cpu_has(X86_FEATURE_PTI))
 			return sprintf(buf, "Mitigation: PTI\n");
+
+		if (hypervisor_is_type(X86_HYPER_XEN_PV))
+			return sprintf(buf, "Unknown (XEN PV detected, hypervisor mitigation required)\n");
 
 		break;