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Shutemov" To: Jia He Cc: Catalin Marinas , Will Deacon , Mark Rutland , James Morse , Marc Zyngier , Matthew Wilcox , "Kirill A. Shutemov" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Suzuki Poulose , Punit Agrawal , Anshuman Khandual , Alex Van Brunt , Robin Murphy , Thomas Gleixner , Andrew Morton , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ralph Campbell , hejianet@gmail.com, Kaly Xin , nd@arm.com Subject: Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190920142113.52mdiflo4yghlsmu@box> References: <20190920135437.25622-1-justin.he@arm.com> <20190920135437.25622-4-justin.he@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190920135437.25622-4-justin.he@arm.com> User-Agent: NeoMutt/20180716 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote: > When we tested pmdk unit test [1] vmmalloc_fork TEST1 in arm64 guest, there > will be a double page fault in __copy_from_user_inatomic of cow_user_page. > > Below call trace is from arm64 do_page_fault for debugging purpose > [ 110.016195] Call trace: > [ 110.016826] do_page_fault+0x5a4/0x690 > [ 110.017812] do_mem_abort+0x50/0xb0 > [ 110.018726] el1_da+0x20/0xc4 > [ 110.019492] __arch_copy_from_user+0x180/0x280 > [ 110.020646] do_wp_page+0xb0/0x860 > [ 110.021517] __handle_mm_fault+0x994/0x1338 > [ 110.022606] handle_mm_fault+0xe8/0x180 > [ 110.023584] do_page_fault+0x240/0x690 > [ 110.024535] do_mem_abort+0x50/0xb0 > [ 110.025423] el0_da+0x20/0x24 > > The pte info before __copy_from_user_inatomic is (PTE_AF is cleared): > [ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003, pmd=000000023d4b3003, pte=360000298607bd3 > > As told by Catalin: "On arm64 without hardware Access Flag, copying from > user will fail because the pte is old and cannot be marked young. So we > always end up with zeroed page after fork() + CoW for pfn mappings. we > don't always have a hardware-managed access flag on arm64." > > This patch fix it by calling pte_mkyoung. Also, the parameter is > changed because vmf should be passed to cow_user_page() > > Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error > in case there can be some obscure use-case.(by Kirill) > > [1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork > > Reported-by: Yibo Cai > Signed-off-by: Jia He Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov