linux-kernel - RE: [PATCH] x86/memcpy: Introduce memcpy_mcsafe

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Message-ID: <3908561D78D1C84285E8C5FCA982C28F7F5FB29E@ORSMSX115.amr.corp.intel.com>
Date:   Mon, 20 Apr 2020 20:57:37 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>
CC:     Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        stable <stable@...r.kernel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Tsaur, Erwin" <erwin.tsaur@...el.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: RE: [PATCH] x86/memcpy: Introduce memcpy_mcsafe_fast

>  (a) is a trap, not an exception - so the instruction has been done,
> and you don't need to try to emulate it or anything to continue.

Maybe for errors on the data side of the pipeline. On the instruction
side we can usually recover from user space instruction fetches by
just throwing away the page with the corrupted instructions and reading
from disk into a new page. Then just point the page table to the new
page, and hey presto, its all transparently fixed (modulo time lost fixing
things).

-Tony