linux-kernel - Re: [PATCH v2] mm, hwpoison: Try to recover from copy-on write faults

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Date:   Sun, 23 Oct 2022 23:04:22 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     "Luck, Tony" <tony.luck@...el.com>,
        David Laight <David.Laight@...LAB.COM>
Cc:     Naoya Horiguchi <naoya.horiguchi@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] mm, hwpoison: Try to recover from copy-on write faults



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