Re: [Xen-devel] IOREQ server on Arm

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.09.18 at 12:51, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
>> From: Julien Grall [mailto:julien.grall@xxxxxxx]
>> Sent: 26 September 2018 11:41
>> To: Jan Beulich <JBeulich@xxxxxxxx>; Paul Durrant
>> <Paul.Durrant@xxxxxxxxxx>
>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Roger Pau Monne
>> <roger.pau@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; xen-
>> devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
>> Subject: Re: IOREQ server on Arm
>> 
>> Hi Jan,
>> 
>> On 09/26/2018 09:08 AM, Jan Beulich wrote:
>> >>>> On 26.09.18 at 00:39, <julien.grall@xxxxxxx> wrote:
>> >> Hi Paul,
>> >>
>> >> I am looking at porting the IOREQ server infrastructure on Arm. I
>> didn't
>> >> need much modification to make it run for Arm. Although, the
>> >> implementation could be simplified over the x86 implementation.
>> >>
>> >> I noticed some issue while trying to implement the hypercall
>> >> XENMEM_acquire_resource. Per my understanding, all the page mapped via
>> >> that hypercall will use the type p2m_mapping_foreign.
>> >>
>> >> This will result to trigger the ASSERT(fdom != dom) in
>> get_page_from_gfn
>> >> (asm-arm/p2m.h) because the IOREQ page has been allocated to the
>> >> emulator domain and mapped to it. AFAICT x86 has the same assert in
>> >> p2m_get_page_from_gfn(...).
>> >>
>> >> IHMO, the ASSERT makes sense because you are only meant to map page
>> >> belonging to other domain with that type.
>> >>
>> >> So I am wondering whether IOREQ server running in PVH Dom0 has been
>> >> tested? What would be the best course of action to fix the issue?
>> >
>> > I think the p2m type needs to be chosen based on
>> > XENMEM_rsrc_acq_caller_owned.
>> 
>> I am thinking to introduce p2m_mapping_owned. Or do we have a p2m_type
>> that we could re-use?
>> 
> 
> I think we should be able to just use p2m_ram_rw if it is caller owned.

Yes, that's what I too would have thought. If there ever was a resource
which may only be mapped r/o, p2m_ram_ro should then be equally usable.

Jan



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