On Mon, 2018-02-26 at 20:53 +0800, Hanjun Guo wrote: > On 2018/2/26 19:04, Will Deacon wrote: > > 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 > > Sorry, just back from holidays and didn't catch up with all the emails, > thanks for taking care of this.
I will work on a fix for the common/x86 code. Thanks, -Toshi
