Re: [Xen-devel] workaround for dom0 crash due to QEMU using O_DIRECT

[George Dunlap <dunlapg@xxxxxxxxx>]

On Mon, Jul 8, 2013 at 8:40 PM, Alex Bligh <alex@xxxxxxxxxxx> wrote:
>
>
> --On 8 July 2013 15:18:53 -0400 Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
>
>>> speaking with Ian about the dom0 kernel crash caused by using O_DIRECT
>>> in QEMU, we came up with a simple workaround that should turn the crash
>>> into a data corruption problem (same as native).
>>
>>
>> <chuckles> You should for fun also do 0xEE on the 'trade_page' whenever
>> we update the PTE. That way we can detect the corruption as by default
>> the trade_page would be 00.
>
>
> Ha ha I've just read the patch. If I read right, what happens is there's
> a fixed 'junk' page which gets mapped in whenever the granted page gets
> mapped out.
>
> Let's put aside the minor issue here that we've got a kernel patch
> which doesn't actually fix the kernel's problem :-)

It is a bit weird.  :-)  But what it actually does is make the
behavior of the bug running on Xen the same as the behavior of the bug
on other systems.  On bare metal, the contents of a random page will
be sent during the "retransmit" phase.  At the moment, under Xen, it
crashes.  This makes it send random data instead.

 -George

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