Re: [Xen-devel] [PATCH v8 13/14] tools/libxl: explicitly grant access to needed I/O-memory ranges

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.06.14 at 16:31, <ian.campbell@xxxxxxxxxx> wrote:
> On Mon, 2014-05-26 at 12:15 +0100, Jan Beulich wrote:
>> >>> IHMO, the guest doesn't need to have permission to this region. When
>> >>> QEMU ask to map this region to the guest, the hypercall will only check
>> >>> the permission on the domain where QEMU is running. Therefore, the
>> >>> permission should be given to the stubdomain.
>> >>
>> >> How would qemu be involved in I/O from/to a passed through
>> >> device?
>> > 
>> > AFAIU, the mapping of the range 0xa0000-* will be done by QEMU for an 
>> > HVM guest (i.e calling xc_domain_memory_mapping).
>> 
>> If qemu is mapping this _machine_ range to every guest (or every
>> guest getting a GFX device passed through) that would be wrong
>> then too afaict.
> 
> How does this work today then? Do no guests get access to 0xa0000 or do
> we some how determine which of the multiple GFX devices is the primary
> one (with the real 0xa0000 mapped to it)?

I don't know. All that is clear is that the way it is being proposed here
(no matter whether that's a copy of current qemu behavior) can't be
right.

> I can't see 0xa0000 mapped by anything in xen.git and there are too many
> hits on the qemu tree for me to spot it if it is there.

Right - that's all I can tell too.

Jan


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