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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <1557824407-19092-4-git-send-email-anshuman.khandual@arm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Tue, 14 May 2019 09:20:29 +0000 (UTC) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190514_022030_064463_F2F2A3AB X-CRM114-Status: GOOD ( 28.99 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, mhocko@suse.com, ira.weiny@intel.com, robin.murphy@arm.com, cai@lca.pw, logang@deltatee.com, james.morse@arm.com, cpandya@codeaurora.org, arunks@codeaurora.org, dan.j.williams@intel.com, mgorman@techsingularity.net, osalvador@suse.de Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 14.05.19 11:00, Anshuman Khandual wrote: > From: Mark Rutland > > The arm64 ptdump code can race with concurrent modification of the > kernel page tables. At the time this was added, this was sound as: > > * Modifications to leaf entries could result in stale information being > logged, but would not result in a functional problem. > > * Boot time modifications to non-leaf entries (e.g. freeing of initmem) > were performed when the ptdump code cannot be invoked. > > * At runtime, modifications to non-leaf entries only occurred in the > vmalloc region, and these were strictly additive, as intermediate > entries were never freed. > > However, since commit: > > commit 324420bf91f6 ("arm64: add support for ioremap() block mappings") > > ... it has been possible to create huge mappings in the vmalloc area at > runtime, and as part of this existing intermediate levels of table my be > removed and freed. > > It's possible for the ptdump code to race with this, and continue to > walk tables which have been freed (and potentially poisoned or > reallocated). As a result of this, the ptdump code may dereference bogus > addresses, which could be fatal. > > Since huge-vmap is a TLB and memory optimization, we can disable it when > the runtime ptdump code is in use to avoid this problem. I wonder if there is another way to protect from such a race happening. (IOW, a lock). But as you say, it's a debug feature, so this is an easy fix. Looks good to me (with limited arm64 code insight :) ) > > Fixes: 324420bf91f60582 ("arm64: add support for ioremap() block mappings") > Signed-off-by: Mark Rutland > Signed-off-by: Anshuman Khandual > Cc: Ard Biesheuvel > Cc: Catalin Marinas > Cc: Will Deacon > --- > arch/arm64/mm/mmu.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index ef82312..37a902c 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -955,13 +955,18 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys) > > int __init arch_ioremap_pud_supported(void) > { > - /* only 4k granule supports level 1 block mappings */ > - return IS_ENABLED(CONFIG_ARM64_4K_PAGES); > + /* > + * Only 4k granule supports level 1 block mappings. > + * SW table walks can't handle removal of intermediate entries. > + */ > + return IS_ENABLED(CONFIG_ARM64_4K_PAGES) && > + !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); > } > > int __init arch_ioremap_pmd_supported(void) > { > - return 1; > + /* See arch_ioremap_pud_supported() */ > + return !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); > } > > int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot) > -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel