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

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Date:   Mon, 20 Apr 2020 20:45:33 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     "Williams, Dan J" <dan.j.williams@...el.com>,
        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

> By "asynchronous" I don't mean "hours later".
>
> Make it be "interrupts are enabled, before serializing instruction".
>
> Yes, we want bounded error handling latency. But that doesn't mean "synchronous"

Another X86 vendor seems to be adding something like that. See MCOMMIT
in https://www.amd.com/system/files/TechDocs/24594.pdf

But I wonder how an OS will know whether it is running some smart
MCOMMIT-aware application that can figure out what to do with bad
data, or a legacy application that should probably be stopped before
it hurts somebody.

I also wonder how expensive MCOMMIT is (since it is essentially
polling for "did any errors happen").

-Tony