Re: [Xen-devel] [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 06/01/2015 19:26, Andy Lutomirski wrote:
> Don't you stil need:
> 
> version++;
> write the rest;
> version++;
> 
> with possible smp_wmb() in there to keep the compiler from messing around?

No, see my other reply.

Separating the version write is a real bug, but that should be all that
it's needed.

> Also, if you do this, can you also make setting and clearing
> STABLE_BIT properly atomic across all vCPUs?  Or at least do something
> like setting it last and clearing it first on vPCU 0?

That would be nice if you want to make the pvclock area fit in a single
page.  However, it would have to be a separate flag bit, or a separate
CPUID feature.

Paolo

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