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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 01/07/14 17:57, Stefano Stabellini wrote:
> On Tue, 1 Jul 2014, 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.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Thanks. Just a quick follow-up on your question on IRC.

LPAE supports up to 48 bits on ARMv8 (40 bits on v7), so the MFN will 
just fit in 32 bits.
I'm a bit worry about what happen if there is an error? The current 
hypercall doesn't look like to be safe for that. Indeed, the return 
value is used to store the higher gpfn. If the guest also use internal 
error, then we are screw.
This is mostly an issue when the toolstack is running in 32 bits guest 
on 64 bits hypervisor. How x86 support this case?
Stefano was suggesting to introduce a new hypercall 
XENMEM_maximum_gpfn_v2 which will take a pointer to a gpfn in parameter.
Regards,

--
Julien Grall

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