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b=ksB29H8uVe9rbz6Gc3I/RVLHmi05Gz3NqUos+mLcVCNekHM+MZOm0XUkDQI5DarXF AGv5aS8KkH5aAIQ7PicKHbMFdvarEjksWRD/xpHwnPHgIeB4vHyjOE/Zua30T5jm1g 0XKOTlhgJPYIyXoNnBl9vFc4afkCqyNeKeKVuhi/9waELKTJCtwc6rFIt01yIdExYe hJ3ARJqkLA4VKJnXqPW5nxiq1mCAS4bQMYyeuZDuZFn6Kzz8U5XMF0YV5y07Z3pEJ1 zAOUUzOx+uU+Hu264wxZu5kAJpm62MXtco2vVEXJfxpa1OCULmBMvBiPaHZFjSKBJl Nt0ZOSHtCPv9w== Date: Tue, 8 Jul 2025 11:57:47 -0400 From: Sasha Levin To: Suren Baghdasaryan Cc: David Hildenbrand , Andrew Morton , peterx@redhat.com, aarcange@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/userfaultfd: fix missing PTE unmap for non-migration entries Message-ID: References: <20250630031958.1225651-1-sashal@kernel.org> <20250630175746.e52af129fd2d88deecc25169@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6E6E61C000E X-Stat-Signature: 3zk4azcn69hawzppworgjrtepca56sm5 X-Rspam-User: X-HE-Tag: 1751990274-865956 X-HE-Meta: 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 o7Q1OfSg cpl+QEDPlh86HK+p1ENHLw0ktLSBGRlzmPOAhvvp2hECumyLjtiVs++UORPses8Bnip4ygcwd/vWJ5BwoBphEOO7MiWzBEyaPzlcF3lKNl/ERQHhBWZiFoeeOh3mVSsKWHSzkNDEW1NVwvVDqDLCVMhb9IdVgeTGp/u20nTCVSSmQHQpcQ1Jxsgq+/VO0j3q6coBog13BfAxnY8PauafDxx1hvnMNruQ1xybKKYUx4y08s3OJ4oK/L0ormp6nNKj8PngiDVybUgkp2U7GNTzVI6jG+7mmFcYPsAecxaJtvU7AaiwMm7t4GQQ8N62FN/Fr9dWlEQXntpHdIY3EjvVVvyIuXBhRtspdO882VXGLh+aIUChjg+HV4reIY+4i3mqMIhBC7bh+rQE6lkZVwUqDVTQZKf/Ilr49EOL1 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: List-Subscribe: List-Unsubscribe: On Tue, Jul 08, 2025 at 08:39:47AM -0700, Suren Baghdasaryan wrote: >On Tue, Jul 8, 2025 at 8:33 AM Sasha Levin wrote: >> >> On Tue, Jul 08, 2025 at 05:10:44PM +0200, David Hildenbrand wrote: >> >On 01.07.25 02:57, Andrew Morton wrote: >> >>On Sun, 29 Jun 2025 23:19:58 -0400 Sasha Levin wrote: >> >> >> >>>When handling non-swap entries in move_pages_pte(), the error handling >> >>>for entries that are NOT migration entries fails to unmap the page table >> >>>entries before jumping to the error handling label. >> >>> >> >>>This results in a kmap/kunmap imbalance which on CONFIG_HIGHPTE systems >> >>>triggers a WARNING in kunmap_local_indexed() because the kmap stack is >> >>>corrupted. >> >>> >> >>>Example call trace on ARM32 (CONFIG_HIGHPTE enabled): >> >>> WARNING: CPU: 1 PID: 633 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c >> >>> Call trace: >> >>> kunmap_local_indexed from move_pages+0x964/0x19f4 >> >>> move_pages from userfaultfd_ioctl+0x129c/0x2144 >> >>> userfaultfd_ioctl from sys_ioctl+0x558/0xd24 >> >>> >> >>>The issue was introduced with the UFFDIO_MOVE feature but became more >> >>>frequent with the addition of guard pages (commit 7c53dfbdb024 ("mm: add >> >>>PTE_MARKER_GUARD PTE marker")) which made the non-migration entry code >> >>>path more commonly executed during userfaultfd operations. >> >>> >> >>>Fix this by ensuring PTEs are properly unmapped in all non-swap entry >> >>>paths before jumping to the error handling label, not just for migration >> >>>entries. >> >> >> >>I don't get it. >> >> >> >>>--- a/mm/userfaultfd.c >> >>>+++ b/mm/userfaultfd.c >> >>>@@ -1384,14 +1384,15 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, >> >>> entry = pte_to_swp_entry(orig_src_pte); >> >>> if (non_swap_entry(entry)) { >> >>>+ pte_unmap(src_pte); >> >>>+ pte_unmap(dst_pte); >> >>>+ src_pte = dst_pte = NULL; >> >>> if (is_migration_entry(entry)) { >> >>>- pte_unmap(src_pte); >> >>>- pte_unmap(dst_pte); >> >>>- src_pte = dst_pte = NULL; >> >>> migration_entry_wait(mm, src_pmd, src_addr); >> >>> err = -EAGAIN; >> >>>- } else >> >>>+ } else { >> >>> err = -EFAULT; >> >>>+ } >> >>> goto out; >> >> >> >>where we have >> >> >> >>out: >> >> ... >> >> if (dst_pte) >> >> pte_unmap(dst_pte); >> >> if (src_pte) >> >> pte_unmap(src_pte); >> > >> >AI slop? >> >> Nah, this one is sadly all me :( >> >> I was trying to resolve some of the issues found with linus-next on >> LKFT, and misunderstood the code. Funny enough, I thought that the >> change above "fixed" it by making the warnings go away, but clearly is >> the wrong thing to do so I went back to the drawing table... >> >> If you're curious, here's the issue: https://qa-reports.linaro.org/lkft/sashal-linus-next/build/v6.13-rc7-43418-g558c6dd4d863/testrun/29030370/suite/log-parser-test/test/exception-warning-cpu-pid-at-mmhighmem-kunmap_local_indexed/details/ > >Any way to symbolize that Call trace? I can't find build artefacts to >extract vmlinux image... The build artifacts are at https://storage.tuxsuite.com/public/linaro/lkft/builds/2zSrTao2x4P640QKIx18JUuFdc1/ but I couldn't get it to do the right thing. I'm guessing that I need some magical arm32 toolchain bits that I don't carry: cat tr.txt | ./scripts/decode_stacktrace.sh vmlinux <4>[ 38.566145] ------------[ cut here ]------------ <4>[ 38.566392] WARNING: CPU: 1 PID: 637 at mm/highmem.c:622 kunmap_local_indexed+0x198/0x1a4 <4>[ 38.569398] Modules linked in: nfnetlink ip_tables x_tables <4>[ 38.570481] CPU: 1 UID: 0 PID: 637 Comm: uffd-unit-tests Not tainted 6.16.0-rc4 #1 NONE <4>[ 38.570815] Hardware name: Generic DT based system <4>[ 38.571073] Call trace: <4>[ 38.571239] unwind_backtrace from show_stack (arch/arm64/kernel/stacktrace.c:465) <4>[ 38.571602] show_stack from dump_stack_lvl (lib/dump_stack.c:118 (discriminator 1)) <4>[ 38.571805] dump_stack_lvl from __warn (kernel/panic.c:791) <4>[ 38.572002] __warn from warn_slowpath_fmt+0xa8/0x174 <4>[ 38.572290] warn_slowpath_fmt from kunmap_local_indexed+0x198/0x1a4 <4>[ 38.572520] kunmap_local_indexed from move_pages_pte+0xc40/0xf48 <4>[ 38.572970] move_pages_pte from move_pages+0x428/0x5bc <4>[ 38.573189] move_pages from userfaultfd_ioctl+0x900/0x1ec0 <4>[ 38.573376] userfaultfd_ioctl from sys_ioctl+0xd24/0xd90 <4>[ 38.573581] sys_ioctl from ret_fast_syscall+0x0/0x5c <4>[ 38.573810] Exception stack(0xf9d69fa8 to 0xf9d69ff0) <4>[ 38.574546] 9fa0: 00001000 00000005 00000005 c028aa05 b2d3ecd8 b2d3ecc8 <4>[ 38.574919] 9fc0: 00001000 00000005 b2d3ece0 00000036 b2d3ed84 b2d3ed50 b2d3ed7c b2d3ed58 <4>[ 38.575131] 9fe0: 00000036 b2d3ecb0 b6df1861 b6d5f736 <4>[ 38.575511] ---[ end trace 0000000000000000 ]--- -- Thanks, Sasha