Re: [Xen-devel] [PATCH v4 5/7] libxl: support unmapping static shared memory areas during domain destruction

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Wei Liu writes ("Re: [Xen-devel] [PATCH v4 5/7] libxl: support unmapping static 
shared memory areas during domain destruction"):
> On Mon, Feb 12, 2018 at 03:24:26PM +0000, Julien Grall wrote:
> > In any case, the worst that could happen is the unmap is called twice on the
> > same region. So you would get spurious error message. Not that bad.
> 
> Yeah, not that bad. Not going to be a security issue, not going to leak
> resources in the end.
> 
> To avoid spurious unmap, can we maybe unmap the pages after the xenstore
> transaction is committed? In that case, only the successful one gets to
> unmap, the ones that aren't committed will bail.
> 
> (Just tossing around ideas)

It should be the other way around.  Because, your way, if your process
crashes for some reason between the xenstore commit and the unmap, the
memory is leaked.

Instead, do the unmap first.  Check the error code to see if it means
"this was already unmapped" and if so report that only via a debug log
message.

Ian.

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