On Mon, Feb 26, 2018 at 06:57:20PM +0800, Hanjun Guo wrote: > On 2018/2/21 19:57, Will Deacon wrote: > > [sorry, trying to deal with top-posting here] > > > > On Wed, Feb 21, 2018 at 07:36:34AM +0000, Wangxuefeng (E) wrote: > >> The old flow of reuse the 4k page as 2M page does not follow the BBM flow > >> for page table reconstruction，not only the memory leak problems. If BBM flow > >> is not followed，the speculative prefetch of tlb will made false tlb entries > >> cached in MMU, the false address will be got， panic will happen. > > > > If I understand Toshi's suggestion correctly, he's saying that the PMD can > > be cleared when unmapping the last PTE (like try_to_free_pte_page). In this > > case, there's no issue with the TLB because this is exactly BBM -- the PMD > > is cleared and TLB invalidation is issued before the PTE table is freed. A > > subsequent 2M map request will see an empty PMD and put down a block > > mapping. > > > > The downside is that freeing becomes more expensive as the last level table > > becomes more sparsely populated and you need to ensure you don't have any > > concurrent maps going on for the same table when you're unmapping. I also > > can't see a neat way to fit this into the current vunmap code. Perhaps we > > need an iounmap_page_range. > > > > In the meantime, the code in lib/ioremap.c looks totally broken so I think > > we should deselect CONFIG_HAVE_ARCH_HUGE_VMAP on arm64 until it's fixed. > > Simply do something below at now (before the broken code is fixed)? > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index b2b95f7..a86148c 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -84,7 +84,6 @@ config ARM64 > select HAVE_ALIGNED_STRUCT_PAGE if SLUB > select HAVE_ARCH_AUDITSYSCALL > select HAVE_ARCH_BITREVERSE > - select HAVE_ARCH_HUGE_VMAP > select HAVE_ARCH_JUMP_LABEL > select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48) > select HAVE_ARCH_KGDB No, that actually breaks with the use of block mappings for the kernel text. Anyway, see: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=15122ee2c515a253b0c66a3e618bc7ebe35105eb Will -- 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>
