Thanks for your patent review 😊 -- Cheers, Justin (Jia He)
> -----Original Message----- > From: Kirill A. Shutemov <[email protected]> > Sent: 2019年9月20日 22:21 > To: Justin He (Arm Technology China) <[email protected]> > Cc: Catalin Marinas <[email protected]>; Will Deacon > <[email protected]>; Mark Rutland <[email protected]>; James Morse > <[email protected]>; Marc Zyngier <[email protected]>; Matthew > Wilcox <[email protected]>; Kirill A. Shutemov > <[email protected]>; [email protected]; > [email protected]; [email protected]; Suzuki Poulose > <[email protected]>; Punit Agrawal <[email protected]>; > Anshuman Khandual <[email protected]>; Alex Van Brunt > <[email protected]>; Robin Murphy <[email protected]>; > Thomas Gleixner <[email protected]>; Andrew Morton <akpm@linux- > foundation.org>; Jérôme Glisse <[email protected]>; Ralph Campbell > <[email protected]>; [email protected]; Kaly Xin (Arm Technology > China) <[email protected]>; nd <[email protected]> > 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 <[email protected]> > > Signed-off-by: Jia He <[email protected]> > > Acked-by: Kirill A. Shutemov <[email protected]> > > -- > Kirill A. Shutemov
