On Wed, Oct 09, 2019 at 04:42:46PM +0800, Jia He wrote: > When we tested pmdk unit test [1] vmmalloc_fork TEST3 on arm64 guest, there > will be a double page fault in __copy_from_user_inatomic of cow_user_page. > > To reproduce the bug, the cmd is as follows after you deployed everything: > make -C src/test/vmmalloc_fork/ TEST_TIME=60m check > > 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 fixes 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 > > Signed-off-by: Jia He <justin.he@xxxxxxx> > Reported-by: Yibo Cai <Yibo.Cai@xxxxxxx> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> My reviewed-by still stands. Thanks. -- Catalin
