Re: [Xen-devel] [xen-unstable test] 56456: regressions - FAIL

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.05.15 at 12:20, <tim@xxxxxxx> wrote:
> At 12:19 +0100 on 18 May (1431951570), Jan Beulich wrote:
>> >>> On 18.05.15 at 12:50, <roger.pau@xxxxxxxxxx> wrote:
>> > El 18/05/15 a les 12.17, Tim Deegan ha escrit:
>> >>  - have map_dirty_bitmap() DTRT, with something like access_ok() +
>> >>    a linear-pagetable lookup to find the frame.
>> > 
>> > That was my first intention, but AFAICT we have no function in tree to
>> > resolve a PV guest VA into a GFN/MFN. The closest thing I could find was
>> > using guest_walk_tables + guest_walk_to_gfn in order to obtain the gfn.
>> > Should I send a patch to introduce a pv_gva_to_gfn function based on that?
>> 
>> Isn't that what we have the linear page table and guest_map_l1e()
>> for?
> 
> Yes, or in this case guest_get_eff_l1e().  We'd want to make sure we
> get_page() the underlying page as well to guard against it being freed
> and reused while we have a mapping.
> 
> That won't check user/supervisor or write permissions in the upper
> levels of the tree.  OTOH, __copy_to_user() doesn't either, so maybe
> we don't care.

Hmm, permissions are being checked by __copy_to_user() afaict
(due to us using the actual page tables), so that being bypassed
here would seem wrong then.

Jan


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