Re: [Xen-devel] [PATCH v3] x86/p2m: use large pages for MMIO mappings

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2016-01-18 at 09:51 -0700, Jan Beulich wrote:
> > > > On 18.01.16 at 17:32, <ian.campbell@xxxxxxxxxx> wrote:
> > I must confess I'm not entirely following what the various proposals
> > are,
> 
> What is currently implemented by the patch is that, upon error on
> iteration N the hypervisor would clean up on a best effort basis and
> return the error indicator. In the alternative suggested model it
> wouldn't do any cleanup and return N to indicate how far success
> was seen; only in the event that N=0 would an error code be
> returned.
> 
> > but FWIW I have no in-principal problem with the caller (by which I
> > think
> > you mean the tools?)
> 
> Yes.
> 
> > having to cleanup partial success in order to allow
> > incremental attempts to set things up with smaller and smaller page
> > sizes.
> 
> Except that in the new x86 model we're not talking about decreasing
> page size, but just the splitting the hypervisor does in place of true
> preemption. Decreasing page size would actually be harmful to the
> goal of using large pages for the mappings.

Ah, I assumed it was to allow things to progress if no large pages were
actually around. Doing it for preemption purposes sounds ok too I guess.

Ian.


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