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

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Wed, Oct 11, 2006 at 01:15:17PM +0900, Doi.Tsunehisa@xxxxxxxxxxxxxx wrote:
> 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.
Another cpu might see the p2m destruction and mm->pgd != NULL.
Be carefull of memory ordering.
-- 
yamahata

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