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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.10.18 at 16:41, <roger.pau@xxxxxxxxxx> wrote:
> BAR map/unmap is a long running operation that needs to be preempted
> in order to avoid overrunning the assigned vCPU time (or even
> triggering the watchdog).
> 
> Current logic for this preemption is wrong, and won't work at all for
> AMD since only Intel makes use of hvm_io_pending (and even in that
> case the current code is wrong).

I'm having trouble understanding this, both for the AMD aspect
(it is only vvmx.c which has a function call not mirrored on the
AMD side) and for the supposed general brokenness. Without
some clarification I can't judge whether re-implementing via
tasklet is actually the best approach.

> +void vpci_init_vcpu(struct vcpu *v)
> +{
> +    tasklet_init(&v->vpci.task, vpci_process_pending, (unsigned long)v);
>  }

Since there's no respective cleanup code added afaics - what
if the domain gets cleaned up behind the back of the (long
running) tasklet? Don't you want to acquire (and then release)
an extra domain reference somewhere?

Jan



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