Messages in this thread | | | Date | Fri, 19 Nov 2010 19:56:35 +0000 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH] ARM: l2x0: Check the correct address range |
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On Fri, Nov 19, 2010 at 05:30:14AM -0600, Kanigeri, Hari wrote: > > diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c > > index 170c9bb..50599d9 100644 > > --- a/arch/arm/mm/cache-l2x0.c > > +++ b/arch/arm/mm/cache-l2x0.c > > @@ -195,7 +195,7 @@ static void l2x0_clean_range(unsigned long start, unsigned long end) > > void __iomem *base = l2x0_base; > > unsigned long flags; > > > > - if ((end - start) >= l2x0_size) { > > + if ((end - start + 1) >= l2x0_size) { > > nitpick: probably will look more obvious if it is coded as if ((end + > 1) - start) >= l2x0_size)
Start defines the first byte of the object to perform the cache maintainence on. End defines the first subsequent byte not in the object. So, (end - start) is the number of bytes in the object, and therefore the original code _is_ correct.
If you have an object which is 1MB in size, then (end - start) will be 1048576 bytes. If your cache is 1MB, then we'll use the xxx_all() version of the function.
However, things get more murky when you consider that we have the granularity of cache lines to deal with.
If start is mid-way in a cache line, then that cache line has to be operated on. If end is mid-way or at the end of a cache line, that cache line also has to be operated on. However, if end is at the very first byte of the cache line, it must not be operated on.
So, it is possible for start = mid-cache line, end = start + 1048575, that you will end up not doing the xxx_all() optimization, despite operating on over 1MB of cached data - but this is only true for the corner case up to 1MB + cache line size - 1. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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