Re: [Xen-devel] [PATCH v2] x86: invpcid support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.03.18 at 17:23, <wei.liu2@xxxxxxxxxx> wrote:
> +static inline void invpcid(unsigned int pcid, unsigned long addr,
> +                           unsigned int type)
> +{
> +    struct {
> +        uint64_t pcid:12;
> +        uint64_t reserved:52;
> +        uint64_t addr;
> +    } desc = { .pcid = pcid, .addr = addr };
> +
> +    asm volatile (
> +#ifdef HAVE_AS_INVPCID
> +                  "invpcid %[desc], %q[type]"
> +                  : /* No output */
> +                  : [desc] "m" (desc), [type] "r" (type)
> +#else
> +                  INVPCID_OPCODE MODRM_ECX_01
> +                  : /* No output */
> +                  : "a" (type), "c" (&desc)
> +#endif
> +                  : "memory" );

I can see why you need the memory clobber in the #else case
(albeit even there it could be avoided by also properly specifying
the input), but what is this good for in the #if case?

Jan


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