Re: [Xen-devel] [PATCH v12 05/11] x86/mm: add HYPERVISOR_memory_op to acquire guest resources

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Paul,

On 20/10/17 09:26, Paul Durrant wrote:
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > Sent: 20 October 2017 07:25
> > To: Julien Grall <julien.grall@xxxxxxxxxx>
> > Cc: Julien Grall <julien.grall@xxxxxxx>; Andrew Cooper
> > <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap
> > <George.Dunlap@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Paul
> > Durrant <Paul.Durrant@xxxxxxxxxx>; Roger Pau Monne
> > <roger.pau@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Stefano Stabellini
> > <sstabellini@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; Konrad Rzeszutek
> > Wilk <konrad.wilk@xxxxxxxxxx>; Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>;
> > Tim (Xen.org) <tim@xxxxxxx>
> > Subject: Re: [Xen-devel] [PATCH v12 05/11] x86/mm: add
> > HYPERVISOR_memory_op to acquire guest resources
> >
> > > > > On 19.10.17 at 18:21, <julien.grall@xxxxxxxxxx> wrote:
> > > Looking a bit more at the resource you can acquire from this hypercall.
> > > Some of them are allocated using alloc_xenheap_page() so not assigned to
> > > a domain.
> > >
> > > So I am not sure how you can expect a function set_foreign_p2m_entry to
> > > take reference in that case.
> > Hmm, with the domain parameter added, DOMID_XEN there (for
> > Xen heap pages) could identify no references to be taken, if that
> > was really the intended behavior in that case. However, even for
> > Xen heap pages life time tracking ought to be done - it is for a
> > reason that share_xen_page_with_guest() assigns the target
> > domain as the owner of such pages, as that allows get_page() to
> > succeed for them.
> So, nothing I'm doing here is making anything worse, right? Grant tables are 
> assigned to the guest, and IOREQ server pages are allocated with 
> alloc_domheap_page() so nothing is anonymous.
I don't think grant tables is assigned to the guest today. They are 
allocated using xenheap_pages() and I can't find 
share_xen_page_with_guest().
Anyway, I discussed with Stefano about it. set_foreign_p2m_entry is 
going to be left unimplemented on Arm until someone as time to implement 
correctly the function.
Cheers,

--
Julien Grall

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