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Tue, 27 Mar 2018 16:31:38 -0400 Received: from mail-pg0-f68.google.com ([74.125.83.68]:36124 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750966AbeC0Ubg (ORCPT ); Tue, 27 Mar 2018 16:31:36 -0400 X-Google-Smtp-Source: AIpwx4/mKJpfebJRaE3gEHuW4v+nMXiRTealr5aMTbUt16xsWU52CN6LRtpmNHJtolRX2rJo/if9GQ== Date: Tue, 27 Mar 2018 13:31:30 -0700 From: Nathan Chancellor To: Dan Rue Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Lei Li , Toshi Kani , Catalin Marinas , Wang Xuefeng , Will Deacon , Hanjun Guo , Michal Hocko , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov , Matthew Wilcox , Chintan Pandya , Andrew Morton , Linus Torvalds Subject: Re: [PATCH 4.4 20/43] mm/vmalloc: add interfaces to free unmapped page table Message-ID: <20180327203130.GA18921@localhost> References: <20180327162716.407986916@linuxfoundation.org> <20180327162717.580646019@linuxfoundation.org> <20180327201700.xmgzgqox3sz3z32r@xps> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180327201700.xmgzgqox3sz3z32r@xps> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, Mar 27, 2018 at 03:17:00PM -0500, Dan Rue wrote: > On Tue, Mar 27, 2018 at 06:27:24PM +0200, Greg Kroah-Hartman wrote: > > 4.4-stable review patch. If anyone has any objections, please let me know. > > > > ------------------ > > > > From: Toshi Kani > > > > commit b6bdb7517c3d3f41f20e5c2948d6bc3f8897394e upstream. > > > > On architectures with CONFIG_HAVE_ARCH_HUGE_VMAP set, ioremap() may > > create pud/pmd mappings. A kernel panic was observed on arm64 systems > > with Cortex-A75 in the following steps as described by Hanjun Guo. > > > > 1. ioremap a 4K size, valid page table will build, > > 2. iounmap it, pte0 will set to 0; > > 3. ioremap the same address with 2M size, pgd/pmd is unchanged, > > then set the a new value for pmd; > > 4. pte0 is leaked; > > 5. CPU may meet exception because the old pmd is still in TLB, > > which will lead to kernel panic. > > > > This panic is not reproducible on x86. INVLPG, called from iounmap, > > purges all levels of entries associated with purged address on x86. x86 > > still has memory leak. > > > > The patch changes the ioremap path to free unmapped page table(s) since > > doing so in the unmap path has the following issues: > > > > - The iounmap() path is shared with vunmap(). Since vmap() only > > supports pte mappings, making vunmap() to free a pte page is an > > overhead for regular vmap users as they do not need a pte page freed > > up. > > > > - Checking if all entries in a pte page are cleared in the unmap path > > is racy, and serializing this check is expensive. > > > > - The unmap path calls free_vmap_area_noflush() to do lazy TLB purges. > > Clearing a pud/pmd entry before the lazy TLB purges needs extra TLB > > purge. > > > > Add two interfaces, pud_free_pmd_page() and pmd_free_pte_page(), which > > clear a given pud/pmd entry and free up a page for the lower level > > entries. > > > > This patch implements their stub functions on x86 and arm64, which work > > as workaround. > > > > [akpm@linux-foundation.org: fix typo in pmd_free_pte_page() stub] > > Link: http://lkml.kernel.org/r/20180314180155.19492-2-toshi.kani@hpe.com > > Fixes: e61ce6ade404e ("mm: change ioremap to set up huge I/O mappings") > > Reported-by: Lei Li > > Signed-off-by: Toshi Kani > > Cc: Catalin Marinas > > Cc: Wang Xuefeng > > Cc: Will Deacon > > Cc: Hanjun Guo > > Cc: Michal Hocko > > Cc: Thomas Gleixner > > Cc: Ingo Molnar > > Cc: "H. Peter Anvin" > > Cc: Borislav Petkov > > Cc: Matthew Wilcox > > Cc: Chintan Pandya > > Cc: > > Signed-off-by: Andrew Morton > > Signed-off-by: Linus Torvalds > > Signed-off-by: Greg Kroah-Hartman > > This patch causes the following build error on 4.4 arm64: > > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=build-arm64 defconfig > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=build-arm64 > > CC arch/arm64/mm/mmu.o > ../arch/arm64/mm/mmu.c:701:5: error: redefinition of ‘pud_free_pmd_page’ > int pud_free_pmd_page(pud_t *pud) > ^~~~~~~~~~~~~~~~~ > In file included from ../arch/arm64/include/asm/pgtable.h:682:0, > from ../include/linux/mm.h:55, > from ../include/linux/mman.h:4, > from ../arch/arm64/mm/mmu.c:25: > ../include/asm-generic/pgtable.h:777:19: note: previous definition of ‘pud_free_pmd_page’ was here > static inline int pud_free_pmd_page(pud_t *pud) > ^~~~~~~~~~~~~~~~~ > ../arch/arm64/mm/mmu.c:706:5: error: redefinition of ‘pmd_free_pte_page’ > int pmd_free_pte_page(pmd_t *pmd) > ^~~~~~~~~~~~~~~~~ > In file included from ../arch/arm64/include/asm/pgtable.h:682:0, > from ../include/linux/mm.h:55, > from ../include/linux/mman.h:4, > from ../arch/arm64/mm/mmu.c:25: > ../include/asm-generic/pgtable.h:781:19: note: previous definition of ‘pmd_free_pte_page’ was here > static inline int pmd_free_pte_page(pmd_t *pmd) > ^~~~~~~~~~~~~~~~~ > make[2]: *** [../scripts/Makefile.build:270: arch/arm64/mm/mmu.o] Error 1 > make[1]: *** [/home/drue/src/linux/4.4-rc/Makefile:969: arch/arm64/mm] Error 2 > make[1]: Leaving directory '/home/drue/src/linux/4.4-rc/build-arm64' > make: *** [Makefile:152: sub-make] Error 2 > > Both of my arm64 devices built fine with this patch... It seems like the only way to hit that error is if HAVE_ARCH_HUGE_VMAP isn't set, which seems impossible since it is selected by ARM64... Someone smarter than I might have more insight but this patch is unchanged from upstream so I can only assume that this error would manifest there as well. Cheers! Nathan