On Sat, Aug 2, 2014 at 12:10 AM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > 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. Ok, let me try again. >> --- 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. Ok, I'll drop it. > 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. It's not a fix, for xtensa it's a part of a new feature, so no need for backporting. -- Thanks. -- Max -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>