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

Rohit Seth
2007-05-02T00:36:27Z

On Tue, 2007-05-01 at 21:47 +1000, Nick Piggin wrote:
> Rohit Seth wrote:
> >
> >
> > It is invalidating any entries (containing same physical address) in both I
> > and D caches. Any dirty lines in D cache are written back to memory before
> > getting invalidated (ofcourse).
>
> OK. (should it be issuing both fc and fc.i to be robust in case a
> new implementation doesn't flush the dcache with fc.i?)
>

For the Itanium case specifically, you only want to invalidate a stale
icache line. Once that is done, next time icache will pick the correct
updated contents.

>
> >>There are supposedly no icache lines at that point[**]:
> >
> >
> > For this bug to trigger there has to be a (stale) entry in icache containing
> > the old contents of a page that just got updated by kernel as explicit
> > copying of data (DMAs are coherent on ia64, meaning if a device were to
> > write to memory then architecture guarnatees that both I and D caches are
> > invalidated).
>
> So if we have a dirty dcache line for a given physical address,
> it will _always_ be the case that a subsequent icache load will
> find that dirty data?

yes for ia64.

-rohit