Re: [Xen-devel] [PATCH v3 0/3] map grant refs at pfn = mfn

[Thomas Leonard <talex5@xxxxxxxxx>]

On 1 August 2014 17:25, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Fri, 1 Aug 2014, Julien Grall wrote:
>> On 01/08/14 17:16, Thomas Leonard wrote:
>> > On 1 August 2014 16:13, Stefano Stabellini
>> > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> > > On Fri, 1 Aug 2014, Thomas Leonard wrote:
>> > > > On 24/07/14 14:30, Stefano Stabellini wrote:
>> > > > > Hi all,
>> > > > > this patch series introduces a second p2m mapping of grant reference
>> > > > > on
>> > > > > ARM at guest physical address == machine address of the grant ref.  
>> > > > > It
>> > > > > is safe because dom0 is already mapped 1:1. We export
>> > > > > XENFEAT_grant_map_identity to signal the guest that this second p2m
>> > > > > mapping is
>> > > > > available.
>> > > > >
>> > > > > One reason for wanting the second p2m mapping is to avoid tracking 
>> > > > > mfn
>> > > > > to pfn mappings in the guest kernel. Since the same mfn can be 
>> > > > > granted
>> > > > > multiple times to the backend, finding the right pfn corresponding to
>> > > > > a
>> > > > > given mfn can be difficult and expensive. Providing a second mapping
>> > > > > at
>> > > > > a known address allow the kernel to access the page without knowing
>> > > > > the
>> > > > > pfn.
>> > > >
>> > > > Is there a version of these patches for Xen 4.4 that I can test? The
>> > > > restriction on duplicate pages is causing trouble for networking on
>> > > > Mirage too
>> > > > (http://roscidus.com/blog/blog/2014/07/28/my-first-unikernel/#tcp-retransmissions).
>> > >
>> > > The backport is non-trivial because
>> > > 552710b388630dfa461932940a998e120c42277d is missing from 4.4,
>> > > nonetheless it wasn't too hard to port:
>> > >
>> > >    git://xenbits.xen.org/people/sstabellini/xen-unstable.git
>> > > grant_map_identity_4.4
>> >
>> > Thanks. I merged it with the stable-4.4 branch (as that has some
>> > useful fixes too), but it crashed for me when I started my Mirage
>> > guest:
>>
>> You have to drop the BUG_ON line 729.
>
> Yes, you are right

This one too?

(XEN) Xen BUG at grant_table.c:946
(XEN) CPU1: Unexpected Trap: Undefined Instruction


-- 
Dr Thomas Leonard        http://0install.net/
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