Re: [Xen-devel] [PATCH V3] X86/vMCE: handle broken page with regard to migration

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Ian Campbell wrote:
> On Fri, 2012-11-16 at 18:31 +0000, Liu, Jinsong wrote:
>>>> +            /*
>>>> +             * if vMCE occur at last iter, do one more iter so
>>>> that it get +             * chance to transfer broken page's
>>>> pfn_type and pfn number to +             * target and then take
>>>> appropriate action [...] +            }
>>> 
>>> Is this really the best way of doing this ?  Isn't there some single
>>> flag the hypervisor sets somewhere ?
> 
>> That will involve adding new hypercall, and notifying hypervisor
>> whether tools side is at the last iter round.
> 
> If we get to this stage then haven't we either already sent something
> over the wire for this page or marked it as dirty when we tried and
> failed to send it?
> 
> In the former case we don't care that the page is now broken on the
> source since the target has got a good pre-breakage copy.

Yes, and theoritically it's better, if only tools save code and hypervisor vmce 
code can *easily* know status each other, like
* whether vmce occur at last iteration
* whether the broken page is at dirty bitmap or not at last iteration

> 
> In the latter case could we not set a flag at the same time as we mark
> the page dirty which means "go round at least one more time"?
> 
> Ian.

That would involve adding new hypercalls for this corner case.

IMO it's better to keep simple way for the corner case, re-use currently 
existed mechanism.

Thanks,
Jinsong

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