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Message-ID: <b5ff4c70-6379-4cc7-8c92-778d80a6a658@redhat.com> Date: Mon, 11 Mar 2024 15:48:14 +0100 From: David Hildenbrand <david@...hat.com> To: Peter Xu <peterx@...hat.com> Cc: Mirsad Todorovac <mirsad.todorovac@....unizg.hr>, linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org, Axel Rasmussen <axelrasmussen@...gle.com> Subject: Re: BUG selftests/mm] On 11.03.24 15:35, Peter Xu wrote: > On Mon, Mar 11, 2024 at 10:31:41AM +0100, David Hildenbrand wrote: >> On 09.03.24 20:12, Mirsad Todorovac wrote: >>> Hi, >>> >>> Routine run of the test in net-next gave also this mm unit error. >>> >>> root@...iant:tools/testing/selftests/mm# ./uffd-unit-tests >>> Testing UFFDIO_API (with syscall)... done >>> Testing UFFDIO_API (with /dev/userfaultfd)... done >>> Testing register-ioctls on anon... done >>> Testing register-ioctls on shmem... done >>> Testing register-ioctls on shmem-private... done >>> Testing register-ioctls on hugetlb... skipped [reason: memory allocation failed] >>> Testing register-ioctls on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing zeropage on anon... done >>> Testing zeropage on shmem... done >>> Testing zeropage on shmem-private... done >>> Testing zeropage on hugetlb... skipped [reason: memory allocation failed] >>> Testing zeropage on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing move on anon... done >>> Testing move-pmd on anon... done >>> Testing move-pmd-split on anon... done >>> Testing wp-fork on anon... done >>> Testing wp-fork on shmem... done >>> Testing wp-fork on shmem-private... done >>> Testing wp-fork on hugetlb... skipped [reason: memory allocation failed] >>> Testing wp-fork on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing wp-fork-with-event on anon... done >>> Testing wp-fork-with-event on shmem... done >>> Testing wp-fork-with-event on shmem-private... done >>> Testing wp-fork-with-event on hugetlb... skipped [reason: memory allocation failed] >>> Testing wp-fork-with-event on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing wp-fork-pin on anon... done >>> Testing wp-fork-pin on shmem... done >>> Testing wp-fork-pin on shmem-private... done >>> Testing wp-fork-pin on hugetlb... skipped [reason: memory allocation failed] >>> Testing wp-fork-pin on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing wp-fork-pin-with-event on anon... done >>> Testing wp-fork-pin-with-event on shmem... done >>> Testing wp-fork-pin-with-event on shmem-private... done >>> Testing wp-fork-pin-with-event on hugetlb... skipped [reason: memory allocation failed] >>> Testing wp-fork-pin-with-event on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing wp-unpopulated on anon... done >>> Testing minor on shmem... done >>> Testing minor on hugetlb... skipped [reason: memory allocation failed] >>> Testing minor-wp on shmem... done >>> Testing minor-wp on hugetlb... skipped [reason: memory allocation failed] >>> Testing minor-collapse on shmem... done >>> Testing sigbus on anon... done >>> Testing sigbus on shmem... done >>> Testing sigbus on shmem-private... done >>> Testing sigbus on hugetlb... skipped [reason: memory allocation failed] >>> Testing sigbus on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing sigbus-wp on anon... done >>> Testing sigbus-wp on shmem... done >>> Testing sigbus-wp on shmem-private... done >>> Testing sigbus-wp on hugetlb... skipped [reason: memory allocation failed] >>> Testing sigbus-wp on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing events on anon... done >>> Testing events on shmem... done >>> Testing events on shmem-private... done >>> Testing events on hugetlb... skipped [reason: memory allocation failed] >>> Testing events on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing events-wp on anon... done >>> Testing events-wp on shmem... done >>> Testing events-wp on shmem-private... done >>> Testing events-wp on hugetlb... skipped [reason: memory allocation failed] >>> Testing events-wp on hugetlb-private... skipped [reason: memory allocation failed] >>> Testing poison on anon... done >>> Testing poison on shmem... done >>> Testing poison on shmem-private... done >>> Testing poison on hugetlb... skipped [reason: memory allocation failed] >>> Testing poison on hugetlb-private... skipped [reason: memory allocation failed] >>> Userfaults unit tests: pass=42, skip=24, fail=0 (total=66) >>> root@...iant:tools/testing/selftests/mm# grep -i huge /proc/meminfo >>> >>> It resulted in alarming errors in the syslog: >>> >>> Mar 9 19:48:24 defiant kernel: [77187.055103] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4631e000 >>> Mar 9 19:48:24 defiant kernel: [77187.055132] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46320000 >>> Mar 9 19:48:24 defiant kernel: [77187.055160] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46322000 >>> Mar 9 19:48:24 defiant kernel: [77187.055189] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46324000 >>> Mar 9 19:48:24 defiant kernel: [77187.055218] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46326000 >>> Mar 9 19:48:24 defiant kernel: [77187.055250] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46328000 >>> Mar 9 19:48:24 defiant kernel: [77187.055278] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4632a000 >>> Mar 9 19:48:24 defiant kernel: [77187.055307] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4632c000 >>> Mar 9 19:48:24 defiant kernel: [77187.055336] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4632e000 >>> Mar 9 19:48:24 defiant kernel: [77187.055366] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46330000 >>> Mar 9 19:48:24 defiant kernel: [77187.055395] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46332000 >>> Mar 9 19:48:24 defiant kernel: [77187.055423] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46334000 >>> Mar 9 19:48:24 defiant kernel: [77187.055452] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46336000 >>> Mar 9 19:48:24 defiant kernel: [77187.055480] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46338000 >>> Mar 9 19:48:24 defiant kernel: [77187.055509] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4633a000 >>> Mar 9 19:48:24 defiant kernel: [77187.055538] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4633c000 >>> Mar 9 19:48:24 defiant kernel: [77187.055567] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4633e000 >>> Mar 9 19:48:24 defiant kernel: [77187.055597] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46340000 >>> >>> At this point, it can be problem with my box's memory chips, or something with HUGETLB. >>> >>> However, since the "classic" allocations were successful, the problem might be in huge pages, or >>> if I understood well, in deliberate poisoning of pages? >>> >> >> Isn't that just the (expected) side effect of UFFDIO_POISON tests? >> >> IOW, there is no problem here. We are poisoning virtual memory locations >> (not actual memory) and expect a SIGBUS on next access. While testing that, >> we receive these messages. > > Correct. > >> >> The "ugly" thing here seems to be that we can trigger repeated pr_err() from >> user space. There is no rate-limiting in place. Maybe UFFDIO_POISON requires >> root permissions so this cannot be exploited by unprivileged user space to >> flood the system log? >> >> CCing Axel > > This is pretty unfortunate. > > I'm not concerned too much on flooding whoever kicks off the selftests, but > indeed this seems to be able to be used by anyone to trigger such endless > reports in dmesg. Right. > > The issue with requiring a privilege means any hypervisor that will need to > use this to emulate memory errors will also require such privilege, and it > can be a problem. > Yes, we don't want that. > Logically such "hwpoison errors" are not real so it is not needed to be > reported in dmesg, but now we're leveraging it to be exactly the same as a > real hw error to share the code path, iiuc (e.g. on MCE injections). > > One option is to use a different marker reflecting that such hwpoison error > is internal, so we don't need to report in dmesg. That'll also require > (besides another bit in pte markers) one extra VM_FAULT_* flag just for > such reports. Might be slightly an overkill, but I don't see another > better way; not reporting HWPOISON will complicate at least kvm use case > even more. > > Or.. does syslog has its own protection in general for such printk floods? > It'll be easier if that's not a concern to flood then, but I'm not sure > from that regard. From what I know, flooding is considered problematic and we fix it up using "Fixes:" commits. See 1b0a151c10a6d823f033023b9fdd9af72a89591b as one "recent" example. Usually we switch to the _ratelimited() functions, maybe pr_warn_ratelimited() is good enough? But we'd lose some details on a "real" MCE storm, though. -- Cheers, David / dhildenb
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