On 11/16/2015 02:16 PM, Suzuki K. Poulose wrote: > On 13/10/15 09:34, Catalin Marinas wrote: >> On Mon, Oct 12, 2015 at 06:52:56PM +0300, Andrey Ryabinin wrote: >>> Andrey Ryabinin (3): >>> arm64: move PGD_SIZE definition to pgalloc.h >>> arm64: add KASAN support >>> Documentation/features/KASAN: arm64 supports KASAN now >>> >>> Linus Walleij (1): >>> ARM64: kasan: print memory assignment >> >> Patches queued for 4.4. Thanks. >> > > Hi, > > I get the following failure with KASAN + 16K_PAGES + 48BIT_VA, with 4.4-rc1: > > > arch/arm64/mm/kasan_init.c: In function ‘kasan_early_init’: > include/linux/compiler.h:484:38: error: call to ‘__compiletime_assert_95’ declared with attribute error: BUILD_BUG_ON failed: !IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE) > _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) > ^ > include/linux/compiler.h:467:4: note: in definition of macro ‘__compiletime_assert’ > prefix ## suffix(); \ > ^ > include/linux/compiler.h:484:2: note: in expansion of macro ‘_compiletime_assert’ > _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) > ^ > include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’ > #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) > ^ > include/linux/bug.h:74:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’ > BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) > ^ > arch/arm64/mm/kasan_init.c:95:2: note: in expansion of macro ‘BUILD_BUG_ON’ > BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE)); > > > --- > > The problem is that the PGDIR_SIZE is (1UL << 47) with 16K+48bit, which makes > the KASAN_SHADOW_END unaligned(which is aligned to (1UL << (48 - 3)) ). Is the > alignment really needed ? Thoughts on how best we could fix this ? > Yes, it's really needed, because some code relies on this (e.g. clear_pgs() and kasan_init()). But it should be possible to get rid of this requirement. At first we need to rework clear_pgs(). The purpose of clear_pgs() is to remove kasan shadow from swapper_pg_dir. So clear_pgs() should clear the top most kasan_zero_* entries from page tables. Previously it was enough to clear PGDs, in case of 16K_PAGES + 48BIT_VA we probably need to clear PMDs We also have to change following part of kasan_init() ... /* * We are going to perform proper setup of shadow memory. * At first we should unmap early shadow (clear_pgds() call bellow). * However, instrumented code couldn't execute without shadow memory. * tmp_pg_dir used to keep early shadow mapped until full shadow * setup will be finished. */ memcpy(tmp_pg_dir, swapper_pg_dir, sizeof(tmp_pg_dir)); Besides tmp_pg_dir we will need one more temporary page table to store those entries which later will be removed from swapper_pg_dir by clear_pgds(). > Cheers > Suzuki > -- 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>