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

[Yang Hongyang <yanghy@cn.fujitsu.com>]

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@cn.fujitsu.com>
>> Signed-off-by: Wen congyang <wency@cn.fujitsu.com>
>> CC: Andrew Cooper <andrew.cooper3@citrix.com>
>
> 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.