Subject: [PATCH 2/2] arm: cacheflush: Fix user split-caching logic

From: [email-masked] (Steve Capper)
Date: Fri, 13 Dec 2013 12:51:31 +0000

On Fri, Dec 13, 2013 at 12:41:31PM +0000, Steve Capper wrote:
> On Fri, Dec 13, 2013 at 12:06:31PM +0000, Steve Capper wrote:
> > The user split-caching logic in __do_cache_op divides the area to be
> > flushed into interruptable chunks of size PAGE_SIZE. Unfortunately,
> > there is no check to see whether or not the range to be flushed is
> > smaller than the chunk size.
> > 
> > This can result cache flushes for larger ranges than intended,
> > which can result in the flush failing with a -EFAULT. I've observed
> > slowdown and failure with the icache-hygiene test from libhugetlbfs.
> > 
> > This patch fixes the problem by replacing chunk with the minimum of
> > PAGE_SIZE or (end - start), thus we do not overflush.
> > 
> > Signed-off-by: Steve Capper <[email-masked]>
> 
> Gah, apologies. The min should be placed within the loop not before
> as one may not have an exact multiple of chunk size to flush.
> 
> Please ignore this patch, I'll resend an improved version.
> 
> Cheers,
> --
> Steve

... or refer to this one:
http://lists.infradead.org/pipermail/linux-arm-kernel/2013-December/216597.html

Apologies for the noise.

The first patch in the series (fix for compound page flushing),
however, is still pertinent.

Cheers,
-- 
Steve

> 
> > ---
> >  arch/arm/kernel/traps.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> > index 8fcda14..5d3c455 100644
> > --- a/arch/arm/kernel/traps.c
> > +++ b/arch/arm/kernel/traps.c
> > @@ -503,7 +503,7 @@ static inline int
> >  __do_cache_op(unsigned long start, unsigned long end)
> >  {
> >  	int ret;
> > -	unsigned long chunk = PAGE_SIZE;
> > +	unsigned long chunk = min(end - start, PAGE_SIZE);
> >  
> >  	do {
> >  		if (signal_pending(current)) {
> > -- 
> > 1.8.1.4
> >