Re: [Xen-devel] [v2 06/11] vmx: add help functions to support PML

[Kai Huang <kai.huang@xxxxxxxxxxxxxxx>]

On 04/24/2015 03:30 PM, Jan Beulich wrote:
> > > > On 24.04.15 at 08:32, <kai.huang@xxxxxxxxxxxxxxx> wrote:
> > On 04/17/2015 03:37 PM, Jan Beulich wrote:
> > > > > > On 17.04.15 at 09:23, <kai.huang@xxxxxxxxxxxxxxx> wrote:
> > > > I see. I will do as you suggested:
> > > >
> > > > ASSERT((v == current) || (!vcpu_runnable(v) && !v->is_running));
> > > >
> > > > And v != current should be the only case requires the vcpu to be paused.
> > > But if you require (or at least expect) the vCPU to be paused, this
> > > isn't what I suggested. Afaict
> > >
> > > ASSERT((v == current) || (!v->is_running && atomic_read(v->pause_count)));
> > >
> > > would then be the right check (and, while not be a full guarantee that
> > > things wouldn't change behind your back, would at least increase
> > > chances that the vCPU's runnable state won't change, as the vCPU
> > > could have been non-runnable for reasons other than having been
> > > paused).
> > Hi Jan,
> >
> > I tried the ASSERT with atomic_read(&v->pause_count), and it turns out
> > the ASSERT would fail and panic Xen. The reason is domain_pause only
> > increases d->pause_count, but it doesn't internally increase
> > v->pause_count for all vcpus.
> >
> > vmx_vcpu_flush_pml_buffer is only supposed to be called from PML buffer
> > full VMEXIT, and vmx_domain_flush_pml_buffer, before which domain_pause
> > should be called.
> >
> > Sorry that obviously I had some misunderstanding regarding to "require
> > (or at least expect) vCPU to be paused", and looks !vcpu_runnable(v) is
> > the right choice.
> >
> > What's your opinion?
> Then either go with the slightly weaker original (still quoted at the
> top) or (preferred by me) OR together both pause counts in the
> condition.
Thanks. Then I'd like to use original weaker one (below) instead of 
explicitly doing OR 'd->pause_count' and 'v->pause_count', as you are 
not objecting the former :)
ASSERT((v == current) || (!vcpu_runnable(v) && !v->is_running));

Thanks,
-Kai
> Jan
>
>
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