[PATCH] x86: hide MWAITX from PV domains

[PATCH] x86: hide MWAITX from PV domains

[Jan Beulich]

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>

--- a/xen/arch/x86/traps.c
+++ b/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) */
--- a/xen/include/asm-x86/cpufeature.h
+++ b/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 */

Re: [PATCH] x86: hide MWAITX from PV domains

[Andrew Cooper]

On 13/10/15 13:25, Jan Beulich wrote:
> 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.)

This is surely a Linux bug which wants fixing as well?

>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

>
> --- a/xen/arch/x86/traps.c
> +++ b/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) */
> --- a/xen/include/asm-x86/cpufeature.h
> +++ b/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 */
>
>
>

Re: [PATCH] x86: hide MWAITX from PV domains

[Jan Beulich]

>>> On 13.10.15 at 15:15, <andrew.cooper3@citrix.com> wrote:
> On 13/10/15 13:25, Jan Beulich wrote:
>> 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.)
> 
> This is surely a Linux bug which wants fixing as well?

I don't think that's a bug - I cannot see it being invalid to have
MWAITX but not MWAIT. That's just pretty unlikely.

Jan