Re: [Qemu-devel] Memory region allocation races

[Andrey Korolyov]

On Wed, Feb 17, 2016 at 6:30 PM, Igor Mammedov <address@hidden> wrote:
> On Wed, 17 Feb 2016 15:22:29 +0300
> Andrey Korolyov <address@hidden> wrote:
>
>> Hello Igor, everyone,
>>
>> we are seemingly running into the issue with "virtio: error trying to
>> map MMIO memory" on a 'legacy' vhost-net with 64 regions on VMs with
>> relatively small amount of DIMMs, less than ten of 512Mb and larger
>> ones for which it could appear literally on every boot. I could
>> suggest to link the problem to the memory fragmentation as busier
>> hypervisors tending to halt VM more frequently on this error, though
>> it is still a very rare issue and could not be reproduced
>> deterministically. Also there seems to be a (very unobvious) link to
>> the CVE-2015-5307, because we started seeing these stops more
>> frequently after rolling in an appropriate patch. Before it we saw
>> this stop for good once per 1M machine-hours and now it appears ~20
>> times more frequent all across the infrastructure. Could
>> 4de7255f7d2be5e51664c6ac6011ffd6e5463571 +
>> 1e0994730f772580ff98754eb5595190cdf371ef
> These commit are more related to supporting more than 64 regions,
> so it's unlikely that it would fix the issue.
>
> What version of QEMU are you using?
> Do you have following QEMU series applied?
>  [PATCH 0/6] virtio: handle non contigious s/g entries
> It's probably what you are missing.
>

Thanks, I`ve missed this queue back in time!