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

[George Dunlap <george.dunlap@eu.citrix.com>]

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