Thanks for your patent review 😊 -- Cheers, Justin (Jia He) > -----Original Message----- > From: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> > Sent: 2019年9月20日 22:21 > To: Justin He (Arm Technology China) <Justin.He@xxxxxxx> > Cc: Catalin Marinas <Catalin.Marinas@xxxxxxx>; Will Deacon > <will@xxxxxxxxxx>; Mark Rutland <Mark.Rutland@xxxxxxx>; James Morse > <James.Morse@xxxxxxx>; Marc Zyngier <maz@xxxxxxxxxx>; Matthew > Wilcox <willy@xxxxxxxxxxxxx>; Kirill A. Shutemov > <kirill.shutemov@xxxxxxxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; Suzuki Poulose > <Suzuki.Poulose@xxxxxxx>; Punit Agrawal <punitagrawal@xxxxxxxxx>; > Anshuman Khandual <Anshuman.Khandual@xxxxxxx>; Alex Van Brunt > <avanbrunt@xxxxxxxxxx>; Robin Murphy <Robin.Murphy@xxxxxxx>; > Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Andrew Morton <akpm@linux- > foundation.org>; Jérôme Glisse <jglisse@xxxxxxxxxx>; Ralph Campbell > <rcampbell@xxxxxxxxxx>; hejianet@xxxxxxxxx; Kaly Xin (Arm Technology > China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx> > Subject: Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is > cleared > > 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 <Yibo.Cai@xxxxxxx> > > Signed-off-by: Jia He <justin.he@xxxxxxx> > > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > -- > Kirill A. Shutemov
