Re: [Xen-devel] [PATCH RFC 3/3] xtf: add minimal HPET functionality test

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Feb 28, 2018 at 09:24:09AM -0700, Jan Beulich wrote:
> >>> On 28.02.18 at 16:37, <roger.pau@xxxxxxxxxx> wrote:
> > On Fri, Feb 23, 2018 at 07:07:18PM +0000, Wei Liu wrote:
> >> On Fri, Feb 23, 2018 at 01:27:43PM +0000, Roger Pau Monne wrote:
> >> > --- a/arch/x86/include/arch/lib.h
> >> > +++ b/arch/x86/include/arch/lib.h
> >> > @@ -392,6 +392,20 @@ static inline void write_xcr0(uint64_t xcr0)
> >> >      xsetbv(0, xcr0);
> >> >  }
> >> >  
> >> > +static inline uint64_t rdtsc(void)
> >> > +{
> >> > +    uint32_t low, high;
> >> > +
> >> > +    asm volatile ("rdtsc" : "=a" (low), "=d" (high));
> >> > +
> >> 
> >> You probably need to add lfence or mfence. See rdtsc_ordered in Xen.
> > 
> > Oh, OK that's news to me. I guess just using a lfence before it
> > should be fine.
> 
> Except that on AMD, without LFENCE made dispatch serializing,
> you'd need MFENCE.

So using just MFENCE will work everywhere since that's more
restrictive than a lfence?

Thanks, Roger.

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