Re: [Xen-devel] [PATCH for-4.10 v2] passthrough/vtd: Don't DMA to the stack in queue_invalidate_wait()

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Tian, Kevin
> Sent: Monday, October 23, 2017 3:05 PM
> 
> > From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> > Sent: Saturday, October 21, 2017 1:55 AM
> >
> > On 20/10/17 08:12, Jan Beulich wrote:
> > >>>> On 19.10.17 at 18:22, <andrew.cooper3@xxxxxxxxxx> wrote:
> > >> DMA-ing to the stack is generally considered bad practice.  In this case,
> if
> > a
> > >> timeout occurs because of a sluggish device which is processing the
> > request,
> > >> the completion notification will corrupt the stack of a subsequent
> > deeper call
> > >> tree.
> > >>
> > >> Place the poll_slot in a percpu area and DMA to that instead.
> > >>
> > >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > > Please could you extend the commit message to state the issue
> > > remaining with using a single per-CPU slot? With that
> > > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> >
> > How about this?
> >
> > Note: This change does not address other issues with the current
> > implementation, such as once a timeout has been suffered, subsequent
> > completions can't be correlated with their requests.
> >
> 
> Can you increase the poll data +1 every time when a new wait
> comes?
> 

btw curious whether you observed a real issue or just eye-caught
the problem?
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