On Fri, 25 Jul 2014 23:43:46 +0400 Max Filippov <jcmvbkbc@xxxxxxxxx> wrote: > VIPT cache with way size larger than MMU page size may suffer from > aliasing problem: a single physical address accessed via different > virtual addresses may end up in multiple locations in the cache. > Virtual mappings of a physical address that always get cached in > different cache locations are said to have different colors. > L1 caching hardware usually doesn't handle this situation leaving it > up to software. Software must avoid this situation as it leads to > data corruption. > > One way to handle this is to flush and invalidate data cache every time > page mapping changes color. The other way is to always map physical page > at a virtual address with the same color. Low memory pages already have > this property. Giving architecture a way to control color of high memory > page mapping allows reusing of existing low memory cache alias handling > code. > > Provide hooks that allow architectures with aliasing cache to align > mapping address of high pages according to their color. Such architectures > may enforce similar coloring of low- and high-memory page mappings and > reuse existing cache management functions to support highmem. > > This code is based on the implementation of similar feature for MIPS by > Leonid Yegoshin <Leonid.Yegoshin@xxxxxxxxxx>. > It's worth mentioning that xtensa needs this. What is (still) missing from these changelogs is a clear description of the end-user visible effects. Does it fix some bug? If so what? Is it a performace optimisation? If so how much? This info is the top-line reason for the patchset and should be presented as such. > --- a/mm/highmem.c > +++ b/mm/highmem.c > @@ -28,6 +28,9 @@ > #include <linux/highmem.h> > #include <linux/kgdb.h> > #include <asm/tlbflush.h> > +#ifdef CONFIG_HIGHMEM > +#include <asm/highmem.h> > +#endif Should be unneeded - the linux/highmem.h inclusion already did this. Apart from that it all looks OK to me. I'm assuming this is 3.17-rc1 material, but I am unsure because of the missing end-user-impact info. If it's needed in earlier kernels then we can tag it for -stable backporting but again, the -stable team (ie: Greg) will want so see the justification for that backport.
