Re: [Xen-devel] IOREQ server on Arm

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 09/26/2018 10:14 AM, Paul Durrant wrote:
> > -----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.
I don't understand your last sentence. IOREQ is caller owned and 
therefore should work.
As I said, I don't have any problem with mapping the resource. The 
problem is when unmapping it because the region is set with 
p2m_mapping_foreign. You will reach the ASSERT(fdom != p2m->domain) in 
p2m_get_page_from_gfn.
Regardless the reference problem (we support it on Arm). Can you explain 
how this is working on PVH Dom0 today?
Cheers,

--
Julien Grall

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