Messages in this thread Patch in this message | | | Date | Thu, 20 Apr 2023 10:59:54 +0800 | Subject | Re: [PATCH v2] mm: hwpoison: coredump: support recovery from dump_user_range() | From | Kefeng Wang <> |
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On 2023/4/20 10:03, Jane Chu wrote: > > On 4/19/2023 5:03 AM, Kefeng Wang wrote: >> >> >> On 2023/4/19 15:25, HORIGUCHI NAOYA(堀口 直也) wrote: >>> On Tue, Apr 18, 2023 at 05:45:06PM +0800, Kefeng Wang wrote: >>>> >>>> ... >>>>>> @@ -371,6 +372,14 @@ size_t _copy_mc_to_iter(const void *addr, >>>>>> size_t bytes, struct iov_iter *i) >>>>>> EXPORT_SYMBOL_GPL(_copy_mc_to_iter); >>>>>> #endif /* CONFIG_ARCH_HAS_COPY_MC */ >>>>>> +static void *memcpy_from_iter(struct iov_iter *i, void *to, const >>>>>> void *from, >>>>>> + size_t size) >>>>>> +{ >>>>>> + if (iov_iter_is_copy_mc(i)) >>>>>> + return (void *)copy_mc_to_kernel(to, from, size); >>>>> >>>>> Is it helpful to call memory_failure_queue() if copy_mc_to_kernel() >>>>> fails >>>>> due to a memory error? >>>> >>>> For dump_user_range(), the task is dying, if copy incomplete size, the >>>> coredump will fail and task will exit, also memory_failure will >>>> be called by kill_me_maybe(), >>>> >>>> CPU: 0 PID: 1418 Comm: test Tainted: G M 6.3.0-rc5 >>>> #29 >>>> Call Trace: >>>> <TASK> >>>> dump_stack_lvl+0x37/0x50 >>>> memory_failure+0x51/0x970 >>>> kill_me_maybe+0x5b/0xc0 >>>> task_work_run+0x5a/0x90 >>>> exit_to_user_mode_prepare+0x194/0x1a0 >>>> irqentry_exit_to_user_mode+0x9/0x30 >>>> noist_exc_machine_check+0x40/0x80 >>>> asm_exc_machine_check+0x33/0x40 >>> >>> Is this call trace printed out when copy_mc_to_kernel() failed by >>> finding >>> a memory error (or in some testcase using error injection)? >> >> I add dump_stack() into memory_failure() to check whether the poisoned >> memory is called or not, and the call trace shows it do call >> memory_failure(), but I get confused when do the test. >> >>> In my understanding, an MCE should not be triggered when MC-safe copy >>> tries >>> to access to a memory error. So I feel that we might be talking about >>> different scenarios. >>> >>> When I questioned previously, I thought about the following scenario: >>> >>> - a process terminates abnormally for any reason like segmentation >>> fault, >>> - then, kernel tries to create a coredump, >>> - during this, the copying routine accesses to corrupted page to >>> read. >>> >> Yes, we tested like your described, >> >> 1) inject memory error into a process >> 2) send a SIGABT/SIGBUS to process to trigger the coredump >> >> Without patch, the system panic, and with patch only process exits. >> >>> In this case the corrupted page should not be handled by >>> memory_failure() >>> yet (because otherwise properly handled hwpoisoned page should be >>> ignored >>> by coredump process). The coredump process would exit with failure with >>> your patch, but then, the corrupted page is still left unhandled and can >>> be reused, so any other thread can easily access to it again. >> >> As shown above, the corrupted page will be handled by >> memory_failure(), but what I'm wondering, >> 1) memory_failure() is not always called >> 2) look at the above call trace, it looks like from asynchronous >> interrupt, not from synchronous exception, right? >> >>> >>> You can find a few other places (like __wp_page_copy_user and >>> ksm_might_need_to_copy) >>> to call memory_failure_queue() to cope with such unhandled error pages. >>> So does memcpy_from_iter() do the same? >> >> I add some debug print in do_machine_check() on x86: >> >> 1) COW, >> m.kflags: MCE_IN_KERNEL_RECOV >> fixup_type: EX_TYPE_DEFAULT_MCE_SAFE >> >> CPU: 11 PID: 2038 Comm: einj_mem_uc >> Call Trace: >> <#MC> >> dump_stack_lvl+0x37/0x50 >> do_machine_check+0x7ad/0x840 >> exc_machine_check+0x5a/0x90 >> asm_exc_machine_check+0x1e/0x40 >> RIP: 0010:copy_mc_fragile+0x35/0x62 >> >> if (m.kflags & MCE_IN_KERNEL_RECOV) { >> if (!fixup_exception(regs, X86_TRAP_MC, 0, 0)) >> mce_panic("Failed kernel mode recovery", &m, msg); >> } >> >> if (m.kflags & MCE_IN_KERNEL_COPYIN) >> queue_task_work(&m, msg, kill_me_never); >> >> There is no memory_failure() called when >> EX_TYPE_DEFAULT_MCE_SAFE, also EX_TYPE_FAULT_MCE_SAFE too, >> so we manually add a memory_failure_queue() to handle with >> the poisoned page. >> >> 2) Coredump, nothing print about m.kflags and fixup_type, >> with above check, add a memory_failure_queue() or memory_failure() seems >> to be needed for memcpy_from_iter(), but it is totally different from >> the COW scenario >> >> >> Another question, other copy_mc_to_kernel() callers, eg, >> nvdimm/dm-writecache/dax, there are not call memory_failure_queue(), >> should they need a memory_failure_queue(), if so, why not add it into >> do_machine_check() ? >
What I mean is that EX_TYPE_DEFAULT_MCE_SAFE/EX_TYPE_FAULT_MCE_SAFE is designed to identify fixups which allow in kernel #MC recovery, that is, the caller of copy_mc_to_kernel() must know the source is a user address, so we could add a MCE_IN_KERNEL_COPYIN fro the MCE_SAFE type.
diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c index c4477162c07d..63e94484c5d6 100644 --- a/arch/x86/kernel/cpu/mce/severity.c +++ b/arch/x86/kernel/cpu/mce/severity.c @@ -293,12 +293,11 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs) case EX_TYPE_COPY: if (!copy_user) return IN_KERNEL; - m->kflags |= MCE_IN_KERNEL_COPYIN; fallthrough;
case EX_TYPE_FAULT_MCE_SAFE: case EX_TYPE_DEFAULT_MCE_SAFE: - m->kflags |= MCE_IN_KERNEL_RECOV; + m->kflags |= MCE_IN_KERNEL_RECOV | MCE_IN_KERNEL_COPYIN; return IN_KERNEL_RECOV;
default: then we could drop memory_failure_queue(pfn, flags) from cow/ksm copy, or every Machine Check safe memory copy will need a memory_failure_xx() call.
+Thomas,who add the two types, could you share some comments about this,thanks.
> In the dax case, if the source address is poisoned, and we do follow up > with memory_failure_queue(pfn, flags), what should the value of the > 'flags' be ?
I think flags = 0 is enough to for all copy_mc_xxx to isolate the poisoned page.
Thanks.
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