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Re: [Xen-devel] [PATCH] xen/arm: Implement domain_get_maximum_gpfn

On Wed, Sep 3, 2014 at 10:44 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

On Mon, 2014-09-01 at 17:32 -0400, Julien Grall wrote:
> Hi Ian,
>
> On 16/07/14 12:02, Ian Campbell wrote:
> > I'd much prefer to just have the fix to xc_dom_gnttab_hvm_seed for ARM
> > and continue to punt on this interface until it is actually needed by
> > something unavoidable on the guest side (and simultaneously hope that
> > day never comes...).
>
> This patch is a requirement to make Xen Memory access working on ARM.
> Could you reconsider the possibility to apply this patch on Xen?

Needs more rationale as to why it is required for Xen Memory (do you
mean xenaccess?). I assume I'll find that in the relevant thread once I
get to it?

It's used in a non-critical sanity check for performance reasons, as seen here: https://github.com/tklengyel/xen/blob/arm_memaccess3/xen/common/mem_access.c#L75. Without the sanity check we might attempt to set mem_access permissions on gpfn's that don't exist for the guest. It wouldn't break anything to do that but if we know beforehand that the gpfn is outside the scope of what the guest has we can skip the entire thing.

> For the main concern of this thread (i.e the buggy scratch pfn with
> xc_dom_gnttab_hvm_seed), I wrote a patch to let the architecture decided
> which scrach pfn should be used. I will send the patch next week.

OK.

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