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Re: [Xen-devel] [PATCH v7 2/4] xen/arm: grant: Add another entry to map MFN 1:1 in dom0 p2m

On 05/20/2014 09:51 AM, Ian Campbell wrote:
> On Tue, 2014-05-20 at 09:30 +0200, Roger Pau Monnà wrote:
>> Not sure I'm following what's going on here, are you saying that FreeBSD
>> blkfront uses the same grant ref on two (or more) requests at the same time?
> My understanding was that there were two grant refs to the same mfn,
> which could happen if two threads were doing (direct?) IO to buffers
> which happened to lie on the same page, or with aio etc.

Sorry I wasn't clear on the use-case.

I'm trying to run portsnap on a FreeBSD ARM guest. The first time I load
the software, the guest is sending (in xbd_queue_cb) at the same time
multiple grant with the same IPA (guest address). This will result to
the same MFN from DOM0/Xen POV.

I did a bit of debug, and this come from the same thread. I have virtual
buffer where each page of this buffer pointed to the same physical address.

FreeBSD is asking to write this buffer to the disk but from what I see
it mostly contains garbage (full of 0xc2).

I can't find where this comes and wondering if you have any thoughts.

I was wondering if this things happen on FreeBSD x86.


Julien Grall

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