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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

Does the qemu process associated with this domain get frozen while the
secondary is being reset, or does the process get destroyed and recreated.

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;
>          }
>  


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