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

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

George Dunlap wrote:
> On 21/11/12 11:07, Ian Campbell wrote:
>> On Tue, 2012-11-20 at 18:54 +0000, Liu, Jinsong wrote:
>>> Well, let me elaborate more my thought about broken page occur at
>>> last iter: 
>>> 
>>> Theoretically we can separate 'broken page at last iter' into
>>> several sub-cases, and optimize case by case: 
>>> 1. if the page (which will break at last iter) is not on dirty
>>> bitmap (of last iter) --> do nothing is OK, target will happily run
>>> w/o broken page;  
>>> 2. if the page (which will break at last iter) is on dirty bitmap
>>> (of last iter) 
>>>    2.1 if at last iter, vmce occur after page copy --> do nothing
>>> is OK, target happily run w/o broken page; 
>>>    2.2 if vmce occur beofre pfn_type transfer --> do nothing is OK,
>>> V2 patch has correctly handle the case, target will set p2m broken
>>> correctly;  
>>>    2.3 if vmce occur after pfn_type transfer and before copy page
>>> to target --> we need handle this case; 
>>> 
>>> Practically considering it's rare enough, and code complication, we
>>> handle it in a simple way (not so optimized but enough for real
>>> life):  
>>> - we don't distinguish if the page is in dirty bitmap of last iter;
>>> - we don't prefer adding new hypercall for this corner case,
>>> instead we'd like to re-use currently existed hypercall; 
>>> - if vmce occur at last iter, we do 1~2 more iter.
>> Can't a page break on each "last" iter. i.e. you might actually go
>> around as many times as there are pages in the last batch?
> 
> I think it would be only if the pages break one by one, at just the
> right time -- that seems pretty unlikely. :-)
> 
>   -George

And under the case it still OK w/ V3, keeping iter until the last broken page.

Thanks,
Jinsong
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