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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-07-02 at 10:19 +0100, Julien Grall wrote:
> Hi Ian,
> 
> On 02/07/14 10:12, Ian Campbell wrote:
> > On Tue, 2014-07-01 at 15:57 +0100, Julien Grall wrote:
> >> The function domain_get_maximum_gpfn is returning the maximum gpfn ever
> >> mapped in the guest. We can use d->arch.p2m.max_mapped_gfn for this 
> >> purpose.
> >
> > What is using the result of this hypercall?
> 
> The result is at least used by xc_dom_gnttab_hvm_seed, to get a scratch 
> GFN to initialize grant table.
> 
> IHMO this is buggy on ARM (and x86?), because we could have map 
> everything up to the end of the address space (currently 40 bits).

I wonder if we could find a way to not need this hypercall at all.

Any reason why both arm and x86 can't just use a fixed scratch pfn for
this temporary mapping? Both of them surely have spaces which they can
guarantee won't overlap with anything.

> I plan to rework a bit this code.
> 
> Without this patch, xc_dom_gnttab_hvm_seed will use by mistake the pfn 0 
> (0xffffffff + 1).
> 
> Regards,
> 
> 



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