Re: [Xen-devel] TLB flushing in blktap kernel driver?

["Stephen C. Tweedie" <sct@xxxxxxxxxx>]

Hi,

On Wed, 2006-09-27 at 14:30 +0100, Keir Fraser wrote:
> > However, I can't understand right now why we need the tlb flush here.
> > If we're doing any grant table operations between dom0 and domU, then
> > the HV should be doing the tlb flushes for us, shouldn't it?  And mere
> > SMP synchronisation on a ring buffer requires a physical memory barrier,
> > not a TLB synchronisation (and RING_PUSH_REQUESTS already does a wmb.)
> 
> Grant unmapping certainly guarantees to flush TLB entries.

Right.  I can't see why a simple ring buffer poll would *ever* need to
flush tlbs.  I may be missing something, which is why I asked, but it
looks like this was perhaps just intended to be a memory barrier, in
which case the flush call is entirely superfluous (and a significant
performance hit to boot.)

--Stephen



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