Re: [Xen-ia64-devel] Patch for PV-on-HVM for IPF

[Doi.Tsunehisa@xxxxxxxxxxxxxx]

You (yamahata) said:
>>> Although I haven't dug into its details, I want to check my suspicion.
>>> The relinquishing mm code assumes that there's no racy reference.
>>> So your patch seems too easy and not-SMP-safe to me.
>>> For example, mm->pgd isn't protected.
>>> What do you think?
>> 
>>   You are right. Hypervisor may crash in gnttab_copy code during
>> p2m table destruction in relinquish_mm code.
>> 
>>   At least, mm->pgd should be nullify before destruction of the body
>> of p2m table.
>> 
>>   I'll investigate it.
> 
> Simple setting NULL to mm->pgd before the p2m destruction isn't
> SMP-safe again.

  I think so. I'll study more.

> Another cpu might see the p2m destruction and mm->pgd != NULL.
> Be carefull of memory ordering.

  Thank for your comment.

- Doi

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