Re: [Xen-devel] [PATCH 2/4] xen: introduce grant_map_exists

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.10.14 at 12:42, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Thu, 2 Oct 2014, Tim Deegan wrote:
>> At 11:02 +0100 on 02 Oct (1412244156), Stefano Stabellini wrote:
>> > Check whether an mfn has been granted to a given domain on a target
>> > grant table.
>> 
>> The implementation looks good but I'm concerned about the need for it,
>> since linear scans of busy grant tables could get fairly expensive.
>> 
>> I see in patch 3/4 you add a hypercall to flush caches, taking an mfn
>> range.  Should that not take a gfn range?  That would be the idiomatic
>> interface, and the p2m lookup would tell you whether the guest had
>> appropiate rights.
>> 
>> I suspect, from reading 0/4, that I'm missing something about the
>> tangle of non-IOMMU dom0 operations on ARM. :)
> 
> The hypercall is going to be used to flush foreign pages grant mapped in
> Dom0. Unfortunately dom0 doesn't know the gfn, only the dma address
> (==mfn).

Don't grant maps get entered into the P2M as they get established?

Jan


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