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Date:   Sun, 23 Oct 2022 23:04:22 +0800
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Subject: Re: [PATCH v2] mm, hwpoison: Try to recover from copy-on write faults
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To:     "Luck, Tony" <tony.luck@intel.com>,
        David Laight <David.Laight@ACULAB.COM>
Cc:     Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
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From:   Shuai Xue <xueshuai@linux.alibaba.com>
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在 2022/10/22 AM12:30, Luck, Tony 写道:
>>> But maybe it is some RMW instruction ... then, if all the above options didn't happen ... we
>>> could get another machine check from the same address. But then we just follow the usual
>>> recovery path.
> 
> 
>> Let assume the instruction that cause the COW is in the 63/64 case, aka,
>> it is writing a different cache line from the poisoned one. But the new_page
>> allocated in COW is dropped right? So might page fault again?
> 
> It can, but this should be no surprise to a user that has a signal handler for
> a h/w event (SIGBUS, SIGSEGV, SIGILL) that does nothing to address the
> problem, but simply returns to re-execute the same instruction that caused
> the original trap.
> 
> There may be badly written signal handlers that do this. But they just cause
> pain for themselves. Linux can keep taking the traps and fixing things up and
> sending a new signal over and over.
> 
> In this case that loop may involve taking the machine check again, so some
> extra pain for the kernel, but recoverable machine checks on Intel/x86 switched
> from broadcast to delivery to just the logical CPU that tried to consume the poison
> a few generations back. So only a bit more painful than a repeated page fault.
> 
> -Tony
> 
> 

I see, thanks for your patient explanation :)

Best Regards,
Shuai