Is: [PATCH] x86/paravirt: PTE updates in k(un)map_atomic need to besynchronous, regardless of lazy_mmu mode. Was: Re: [PATCH] x86/paravirt:Partially revert "remove lazy mode in interrupts"

[Konrad Rzeszutek Wilk]

On Mon, Sep 26, 2011 at 09:22:21AM -0700, Jeremy Fitzhardinge wrote:
> On 09/26/2011 06:13 AM, Konrad Rzeszutek Wilk wrote:
> > which has git commit b8bcfe997e46150fedcc3f5b26b846400122fdd9.
> >
> > The unintended consequence of removing the flushing of MMU
> > updates when doing kmap_atomic (or kunmap_atomic) is that we can
> > hit a dereference bug when processing a "fork()" under a heavy loaded
> > machine. Specifically we can hit:
> 
> The patch is all OK, but I wouldn't have headlined it as a "partial
> revert" - the important point is that the pte updates in k(un)map_atomic
> need to be synchronous, regardless of whether we're in lazy_mmu mode.
> 
> The fact that b8bcfe997e4 introduced the problem is interesting to note,
> but only somewhat relevant to the analysis of what's being fixed here.

Good point. How about