Message-ID: <9a9876a2-a2fd-40d9-b215-3e6c8207e711@huawei.com>
Date:   Thu, 20 Apr 2023 23:05:12 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Jane Chu <jane.chu@...cle.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Thomas Gleixner <tglx@...utronix.de>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tong Tiangen <tongtiangen@...wei.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v2] mm: hwpoison: coredump: support recovery from
 dump_user_range()



On 2023/4/20 10:59, Kefeng Wang wrote:
> 
> 
> 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,

Sorry，I forget to set coredump file size :(

The coredump do trigger the do_machine_check() with same m.kflags and 
fixup_type like cow


>>> 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
>>>

so the memcpy_from_iter() from coredump is same as 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.

And I think we need the following change for MCE_SAFE copy to set
MCE_IN_KERNEL_COPYIN.

> 
> 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.

which help use to kill unneeded memory_failure_queue() call, any comments?

> 
> +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 ?
> 

With above diff change, we don't add a memory_failure_queue() into dax too.

Thanks

> 
> I think flags = 0 is enough to for all copy_mc_xxx to isolate the 
> poisoned page.
> 
> Thanks.

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