Re: [Xen-devel] IOREQ server on Arm

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----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.

  Paul

> Cheers,
> 
> --
> Julien Grall
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