x86: hide MWAITX from PV domains

Since MWAIT is hidden too. (Linux starting with 4.3 is making use of
that feature, and is checking for it without looking at the MWAIT one.)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/traps.c

@@ -964,6 +964,7 @@ void pv_cpuid(struct cpu_user_regs *regs)
         __clear_bit(X86_FEATURE_LWP % 32, &c);
         __clear_bit(X86_FEATURE_NODEID_MSR % 32, &c);
         __clear_bit(X86_FEATURE_TOPOEXT % 32, &c);
+        __clear_bit(X86_FEATURE_MWAITX % 32, &c);
         break;
 
     case 0x0000000a: /* Architectural Performance Monitor Features (Intel) */

xen/include/asm-x86/cpufeature.h

@@ -140,6 +140,7 @@
 #define X86_FEATURE_TBM         (6*32+21) /* trailing bit manipulations */
 #define X86_FEATURE_TOPOEXT     (6*32+22) /* topology extensions CPUID leafs */
 #define X86_FEATURE_DBEXT       (6*32+26) /* data breakpoint extension */
+#define X86_FEATURE_MWAITX      (6*32+29) /* MWAIT extension (MONITORX/MWAITX) */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 7 */
 #define X86_FEATURE_FSGSBASE	(7*32+ 0) /* {RD,WR}{FS,GS}BASE instructions */