Re: [PATCH RFC] vm_unmap_aliases: allow callers to inhibit TLB flush

[Jeremy Fitzhardinge]

Nick Piggin wrote:
> On Friday 12 December 2008 12:59, Jeremy Fitzhardinge wrote:
>   
> > Nick Piggin wrote:
> >     
> > > Hi,
> > >
> > > On Friday 12 December 2008 06:05, Jeremy Fitzhardinge wrote:
> > >       
> > > > Hi Nick,
> > > >
> > > > In Xen when we're killing the lazy vmalloc aliases, we're only concerned
> > > > about the pagetable references to the mapped pages, not the TLB entries.
> > > >         
> > > Hm? Why is that? Why wouldn't it matter if some page table page gets
> > > written to via a stale TLB?
> > >       
> > No.  Well, yes, it would, but Xen itself will do whatever tlb flushes
> > are necessary to keep it safe (it must, since it doesn't trust guest
> > kernels).  It's fairly clever about working out which cpus need flushing
> > and if other flushes have already done the job.
> >     
>
> OK. Yeah, then the problem is simply that the guest may reuse that virtual
> memory for another vmap.
>   

Hm.  What you would you think of a "deferred tlb flush" flag (or 
something) to cause the next vmap to do the tlb flushes, in the case the 
vunmap happens in a context where the flushes can't be done?

   J
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