Re: [virtio-dev] [PATCH v3 2/2] virtio-fs: add DAX window

[Stefan Hajnoczi <stefanha@redhat.com>]

On Wed, Jul 17, 2019 at 08:42:58AM -0400, Vivek Goyal wrote:
> On Thu, Jun 27, 2019 at 10:09:16AM -0400, Michael S. Tsirkin wrote:
> 
> [..]
> > Well it allocates resources on the host. If you don't
> > contain qemu then even just allocating virtual memory
> > can make host swap, right? If you contain it then
> > qemu will get killed instead but then you need to tell
> > guest what not to do so as not to get qemu killed.
> 
> How is it different than running a malicious unpriviliged process on host?
> 
> Denial of service should be mitigated by per process resource limits which
> will be true in this case as well.
> 
> I am not sure I understand the concern here.

There is a practical problem that the QEMU process may hit the mmap
limit and be unable to perform its own mmaps due to the DAX Window.  A
limit must be enforced on the host so that QEMU's internal mmaps
succeed.

Stefan

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