Re: [Xen-devel] [PATCH v3 5/7] vpci: fix execution of long running operations

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Nov 08, 2018 at 11:42:35AM +0000, Julien Grall wrote:
> Hi,
> 
> Sorry to jump in the conversation late.
> 
> On 11/8/18 11:29 AM, Roger Pau Monné wrote:
> > > Why would that be? The do_softirq() invocation sits on the exit-
> > > to-guest path, explicitly avoiding any such nesting unless there
> > > was a do_softirq() invocation somewhere in a softirq handler.
> > 
> > It sits on an exit-to-guest path, but the following chunk:
> > 
> > raise_softirq(SCHEDULE_SOFTIRQ);
> > do_softirq();
> > 
> > Would prevent the path from ever reaching the exit-to-guest and
> > nesting on itself, unless the vCPU is marked as blocked, which
> > prevents it from being scheduled thus avoiding this recursion.
> 
> I can't see how the recursion could happen on Arm. So is it an x86 issue?

This is not an issue with the current code, I was just discussing with
Jan how to properly implement vPCI long running operations that need
to be preempted.

Roger.

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