Re: Fw: [PATCH] ia64: race flushing icache in do_no_page path

[Nick Piggin]

Rohit Seth wrote:
> On Tue, 2007-05-01 at 21:52 +1000, Nick Piggin wrote:
>
> > Rohit Seth wrote:
> >
> >
> > > > and 
> > > > it's only interested when it's executable i.e. "lazy_mmu_prot_update"
> > > > is a name concealing some overdesign.
> > >
> > >
> > > You are right that ia64 is only interested in whne the execute permissions
> > > kick in (and FWIW ia64 used to use update_mmu_cache API to do what it is now
> > > doing lazy_mmu_prot_update).  Though the idea was to design an API that any
> > > arch can use to know when ever there is change in protections on a mapping.
> >
> > What I think what we should do is audit flush_icache_page coverage, and
> > convert ia64 to use that (because it needs this to happen _before_ the
> > pte is set).
>
>
> That doesn't address the underlying requirement that arch specific code
> should be told of change in protections. 

But you would add the flush_icache_page_chprot to address that.


> For ia64, you are right that
> it equates to flushing icache in some cases, but this API is more
> generic.

And it is also broken, because it needs to be done before the set_pte
for ia64. It needs to be done where flush_icache_page is done. And on
ia64 it flushes the icache. So I don't understand why ia64 would not
use flush_icache_page but add something completely new "because it is
more generic".


> > All we should need to do is add a pte argument to flush_icache,
>
>
> I'm sure this is doable.  Though it is more of design issue of whether
> that is the right way to do it.  I understand this extra API is
> difficult at this time because of one single consumer.

There is just no point in adding something else if you already have
a hook that seems to do what ia64 wants (or could, with a small amount
of work).

--
SUSE Labs, Novell Inc.
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