linux-kernel - Re: [PATCH v6 0/2] Renovate memcpy_mcsafe with copy_mc_to

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Date:   Tue, 23 Jun 2020 21:25:42 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...hat.com,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Borislav Petkov <bp@...en8.de>, stable@...r.kernel.org,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Erwin Tsaur <erwin.tsaur@...el.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v6 0/2] Renovate memcpy_mcsafe with copy_mc_to_{user,
 kernel}

On Wed, Jun 17, 2020 at 05:31:58PM -0700, Dan Williams wrote:
> No changes since v5 [1], just rebased to v5.8-rc1. No comments since
> that posting back at the end of May either, will continue to re-post
> weekly, I am otherwise at a loss for what else to do to move this
> forward. Should it go through Andrew since it's across PPC and x86?
> Thanks again to Michael for the PPC acks.
> 
> [1]: http://lore.kernel.org/r/159062136234.2192412.7285856919306307817.stgit@dwillia2-desk3.amr.corp.intel.com
> 
> ---
> 
> The primary motivation to go touch memcpy_mcsafe() is that the existing
> benefit of doing slow "handle with care" copies is obviated on newer
> CPUs. With that concern lifted it also obviates the need to continue to
> update the MCA-recovery capability detection code currently gated by
> "mcsafe_key". Now the old "mcsafe_key" opt-in to perform the copy with
> concerns for recovery fragility can instead be made an opt-out from the
> default fast copy implementation (enable_copy_mc_fragile()).
> 
> The discussion with Linus on the first iteration of this patch
> identified that memcpy_mcsafe() was misnamed relative to its usage. The
> new names copy_mc_to_user() and copy_mc_to_kernel() clearly indicate the
> intended use case and lets the architecture organize the implementation
> accordingly.
> 
> For both powerpc and x86 a copy_mc_generic() implementation is added as
> the backend for these interfaces.
> 
> Patches are relative to v5.8-rc1. It has a recent build success
> notification from the kbuild robot and is passing local nvdimm tests.
> 

Looks good to me.   I tested on a Broadwell generation system (i.e.
one of the system you now list as "fragile") and injecting uncorrected
errors into buffers that are then copied using copy_mc_to_kernel()
result in recovered machine checks with the return value correctly
indicating the amount remaining.

Reviewed-by: Tony Luck <tony.luck@...el.com>

-Tony