Re: [Xen-devel] [RFC Patch v4 2/8] ioreq: bump the number of IOREQ page to 4 pages

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Chao Gao [mailto:chao.gao@xxxxxxxxx]
> Sent: 15 December 2017 00:36
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Tim
> (Xen.org) <tim@xxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>;
> xen-devel@xxxxxxxxxxxxx; Jan Beulich <jbeulich@xxxxxxxx>; Ian Jackson
> <Ian.Jackson@xxxxxxxxxx>
> Subject: Re: [RFC Patch v4 2/8] ioreq: bump the number of IOREQ page to 4
> pages
> 
> On Thu, Dec 14, 2017 at 02:50:17PM +0000, Paul Durrant wrote:
> >> -----Original Message-----
> >> >
> >> > Hmm. That looks like it is because the ioreq server pages are not owned
> by
> >> > the correct domain. The Xen patch series underwent some changes
> later in
> >> > review and I did not re-test my QEMU patch after that so I wonder if
> >> > mapping IOREQ pages has simply become broken. I'll investigate.
> >> >
> >>
> >> I have reproduced the problem locally now. Will try to figure out the bug
> >> tomorrow.
> >>
> >
> >Chao,
> >
> >  Can you try my new branch
> http://xenbits.xen.org/gitweb/?p=people/pauldu/xen.git;a=shortlog;h=refs
> /heads/ioreq24?
> >
> >  The problem was indeed that the ioreq pages were owned by the
> emulating domain rather than the target domain, which is no longer
> compatible with privcmd's use of HYPERVISOR_mmu_update.
> 
> Of course. I tested this branch. It works well.
> 
> But, I think your privcmd patch couldn't set 'err_ptr' to NULL when
> calling xen_remap_domain_mfn_array(). It works for the ioreq page is
> allocated right before the bufioreq page, and then they happen to be
> continuous.
> 

I'll have a look at that. The pages should not need to be contiguous MFNs for 
things to work. They will, by design, by mapped so that they are virtually 
contiguous. That's just a convenient way of getting pointers to the buf and 
synchronous structures in QEMU using only a single IOCTL to privcmd.

  Paul

> Thanks
> Chao

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