linux-kernel - Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover from machine checks

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Message-ID: <CALCETrVcj=4sDaEXGNtYuq0kXLm7K9de1catqWPi25ae56g8Jg@mail.gmail.com>
Date:	Fri, 11 Dec 2015 14:26:53 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover
 from machine checks

On Fri, Dec 11, 2015 at 2:20 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Fri, Dec 11, 2015 at 2:17 PM, Luck, Tony <tony.luck@...el.com> wrote:
>>> Also, would it be more straightforward if the mcexception landing pad
>>> looked up the va -> pa mapping by itself?  Or is that somehow not
>>> reliable?
>>
>> If we did get all the above right, then we could have
>> target use virt_to_phys() to convert to physical ...
>> I don't see that this part would be a problem.
>
> virt_to_phys() implies a linear address.  In the case of the use in
> the pmem driver we'll be using an ioremap()'d address off somewherein
> vmalloc space.

There's always slow_virt_to_phys.

Note that I don't fundamentally object to passing the pa to the fixup
handler.  I just think we should try to disentangle that from figuring
out what exactly the failure was.

Also, are there really PCOMMIT-capable CPUs that still forcibly
broadcast MCE?  If, so, that's unfortunate.

--Andy
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