Re: [Xen-devel] [PATCH 02/18] xen/arm: Implement PSCI system suspend call (virtual interface)

[Julien Grall <julien.grall@xxxxxxx>]

Hi Mirela,

On 14/11/2018 12:08, Mirela Simonovic wrote:
> On 11/13/2018 09:32 AM, Andrew Cooper wrote:
> > On 12/11/2018 19:56, Julien Grall wrote:
> > > Hi Andrew,
> > >
> > > On 11/12/18 4:41 PM, Andrew Cooper wrote:
> > > > On 12/11/18 16:35, Mirela Simonovic wrote:
> > > > > > > diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> > > > > > > index e594b48d81..7f8105465c 100644
> > > > > > > --- a/xen/arch/arm/domain.c
> > > > > > > +++ b/xen/arch/arm/domain.c
> > > > > > > @@ -97,6 +97,11 @@ static void ctxt_switch_from(struct vcpu *p)
> > > > > > >         if ( is_idle_vcpu(p) )
> > > > > > >             return;
> > > > > > >
> > > > > > > +    /* VCPU's context should not be saved if its domain is
> > > > > > > suspended */
> > > > > > > +    if ( p->domain->is_shut_down &&
> > > > > > > +        (p->domain->shutdown_code == SHUTDOWN_suspend) )
> > > > > > > +        return;
> > > > > > SHUTDOWN_suspend is used in Xen for other purpose (see
> > > > > > SCHEDOP_shutdown). The other user of that code relies on all the state
> > > > > > to be saved on suspend.
> > > > > We just need a flag to mark a domain as suspended, and I do believe
> > > > > SHUTDOWN_suspend is not used anywhere else.
> > > > > Let's come back on this.
> > > > SHUTDOWN_suspend is used for migration.  Grep for it through the Xen
> > > > tree and you'll find several pieces of documentation, including the
> > > > description of what this shutdown code means.
> > > >
> > > > What you are introducing here is not a shutdown - it is a suspend with
> > > > the intent to resume executing later.  As such, it shouldn't use Xen's
> > > > shutdown infrastructure, which exists mainly to communicate with the
> > > > toolstack.
> > > Would domain pause/unpause be a better solution?
> > Actually yes - that sounds like a very neat solution.
> I believe domain pause will not work here - a domain cannot pause itself, i.e. 
> current domain cannot be paused. This functionality seems to assume that a 
> domain is pausing another domain. Or I missed the point.
Yes domain pause/unpause will not work. However, you can introduce a boolean to 
tell you whether the domain was suspend.
I actually quite like how suspend work for x86 HVM. This is based on 
pause/unpause. Have a look at hvm_s3_{suspend/resume}.
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel