Re: [Xen-devel] IOREQ server on Arm

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 26 September 2018 09:09
> To: Julien Grall <julien.grall@xxxxxxx>; 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
> 
> >>> 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.
> 

Yes, that's correct. There is a FIXME clause in acquire_resource so that that 
only caller owned resources can be mapped by HVM/PVH domains. Thus the new call 
can be used for IOREQ server pages, but not grant frames.

  Paul

> Jan
> 


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