linux-kernel - Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to

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Date:   Tue, 01 May 2018 21:05:48 +0000
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter()

On Tue, May 1, 2018 at 1:55 PM Dan Williams <dan.j.williams@...el.com>
wrote:

> The result of the bypass is that the kernel treats machine checks during
> read as system fatal (reboot) when they could simply be flagged as an
> I/O error, similar to performing reads through the pmem driver. Prevent
> this fatal condition by deploying memcpy_mcsafe() in the fsdax read
> path.

How about just changing the rules, and go the old "Don't do that then" way?

IOW, get rid of the whole idea that MCS errors should be fatal. It's wrong
and pointless anyway.

The while approach seems fundamentally buggered, if you ever want to mmap
one of these things. And don't you want that?

So why continue down a fundamentally broken path?

                  Linus