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Re: [Xen-devel] [PATCH v2] x86/domain_page: implement pure per-vCPU mapping infrastructure

On Fri, Feb 21, 2020 at 02:31:08PM +0100, Jan Beulich wrote:
> On 21.02.2020 13:52, Xia, Hongyan wrote:
> > On Fri, 2020-02-21 at 11:50 +0000, Wei Liu wrote:
> >> On Thu, Feb 06, 2020 at 06:58:23PM +0000, Hongyan Xia wrote:
> >>> +    if ( hashmfn != mfn && !vcache->refcnt[idx] )
> >>> +        __clear_bit(idx, vcache->inuse);
> >>
> >> Also, please flush the linear address here and the other __clear_bit
> >> location.
> > 
> > I flush when a new entry is taking a slot. Yeah, it's probably better
> > to flush earlier whenever a slot is no longer in use.
> Question is whether such individual flushes aren't actually
> more overhead than a single flush covering all previously
> torn down entries, done at suitable points (see the present
> implementation).

I asked to flush because I was paranoid about leaving stale entry after
the slot is reclaimed. I think the address will be flushed when a new
entry is inserted.

So the question would be whether we care about leaving a stale entry in
place until a new one is inserted.


> Jan

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