On Mon, Mar 11, 2024 at 8:12 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > On Mon, Mar 11, 2024 at 03:48:14PM +0100, David Hildenbrand wrote: > > 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@defiant: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@defiant: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. > > Yeah, I didn't consider that previously because I thought leaking MCE > addresses might be a problem. > > But now thinking it again, it'll be great if pr_err_ratelimited() works > here (I think we'd still want to report them with "err" not "warnings", > btw). > > I don't worry too much on MCE storm, as in that case explicit addresses may > not be necessary if the whole system is on risk. What I don't know however > is whether the addresses may still matter if e.g. two continuous MCEs are > reported in a small time window, and whether those addresses are a concern > in that case if some got lost. > > My MCE experience is pretty limited, so I don't have an answer to that. > Maybe it can be verified by proposing a patch like that and see whether > there can be any objections making it rate limtied. I'll leave that to > Axel to decide how to move forward. I'd prefer not to require root or CAP_SYS_ADMIN or similar for UFFDIO_POISON, because those control access to lots more things besides, which we don't necessarily want the process using UFFD to be able to do. :/ Ratelimiting seems fairly reasonable to me. I do see the concern about dropping some addresses though. Perhaps we can mitigate that concern by defining our own ratelimit interval/burst configuration? Another idea would be to only ratelimit it if !CONFIG_DEBUG_VM or similar. Not sure if that's considered valid or not. :) > > -- > Peter Xu >
