path: root/arch/arm64/Kconfig
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authorJia He <justin.he@arm.com>2019-10-11 22:09:39 +0800
committerCatalin Marinas <catalin.marinas@arm.com>2019-10-18 11:11:29 +0100
commit83d116c53058d505ddef051e90ab27f57015b025 (patch)
treefbc2f550a6a8db72eddfc3daee9cfe0cfd65006d /arch/arm64/Kconfig
parentx86/mm: implement arch_faults_on_old_pte() stub on x86 (diff)
mm: fix double page fault on arm64 if PTE_AF is cleared
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@arm.com> Reported-by: Yibo Cai <Yibo.Cai@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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