Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero ioreq page only one time

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

On 06/08/2015 05:46 PM, Andrew Cooper wrote:
> On 08/06/15 04:43, Yang Hongyang wrote:
> > ioreq page contains evtchn which will be set when we resume the
> > secondary vm the first time. The hypervisor will check if the
> > evtchn is corrupted, so we cannot zero the ioreq page more
> > than one time.
> >
> > The ioreq->state is always STATE_IOREQ_NONE after the vm is
> > suspended, so it is OK if we only zero it one time.
> >
> > Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> > Signed-off-by: Wen congyang <wency@xxxxxxxxxxxxxx>
> > CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> The issue here is that we are running the restore algorithm over a
> domain which has already been running in Xen for a while.  This is a
> brand new usecase, as far as I am aware.
Exactly.

> Does the qemu process associated with this domain get frozen while the
> secondary is being reset, or does the process get destroyed and recreated.
What do you mean by reset? do you mean secondary is suspended at checkpoint?

> I have a gut feeling that it would be safer to clear all of the page
> other than the event channel, but that depends on exactly what else is
> going on.  We absolutely don't want to do is have an update to this page
> from the primary with an in-progress IOREQ.
>
> ~Andrew
>
> > ---
> >   tools/libxc/xc_sr_restore_x86_hvm.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/libxc/xc_sr_restore_x86_hvm.c 
> > b/tools/libxc/xc_sr_restore_x86_hvm.c
> > index 6f5af0e..06177e0 100644
> > --- a/tools/libxc/xc_sr_restore_x86_hvm.c
> > +++ b/tools/libxc/xc_sr_restore_x86_hvm.c
> > @@ -78,7 +78,8 @@ static int handle_hvm_params(struct xc_sr_context *ctx,
> >               break;
> >           case HVM_PARAM_IOREQ_PFN:
> >           case HVM_PARAM_BUFIOREQ_PFN:
> > -            xc_clear_domain_page(xch, ctx->domid, entry->value);
> > +            if ( !ctx->restore.buffer_all_records )
> > +                xc_clear_domain_page(xch, ctx->domid, entry->value);
> >               break;
> >           }
> .
--
Thanks,
Yang.

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