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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 02/03/18 16:47, Jan Beulich wrote:
>>>> 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?

This is a tlb flush operation.  I don't think anything good will come
from having other operations reordered around it.

~Andrew

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