Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 16 Feb 2022 19:02:58 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Jue Wang <juew@google.com>
Cc:     "Luck, Tony" <tony.luck@intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
Subject: Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine
 checks
Message-ID: <Yg08Uhg0fZ9xZuP2@zn.tnic>
References: <CAPcxDJ7nriZEJHF6dMPR7tQ+dGuueyRjw1NC+4CbjxiAT_S+ZA@mail.gmail.com>
 <20220208150945.266978-1-juew@google.com>
 <Ygwka++3eipjQzB2@zn.tnic>
 <YgwnqTc8FGG3orcE@agluck-desk3.sc.intel.com>
 <YgzRsfWOmqkNiNI7@zn.tnic>
 <CAPcxDJ4=iknzYbN=b2oQxvJyODkQ_MWEj1wkKEuGwf4HQ3aPZA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAPcxDJ4=iknzYbN=b2oQxvJyODkQ_MWEj1wkKEuGwf4HQ3aPZA@mail.gmail.com>
Precedence: bulk

On Wed, Feb 16, 2022 at 07:50:24AM -0800, Jue Wang wrote:
> My slight reservation is that this suggests all use cases of "REP;
> MOVS*" must take the _ASM_EXTABLE_ form, which is not possible;
> considering "REP; MOVS*" can be exercised from any user space program.

Well, we could try to decode the instructions around rIP when the #MC
is raised and see what caused the MCE and perhaps pick apart which insn
caused it, is it accessing behind the buffer boundaries, etc.

> If there is a way to get all users of "REP; MOVS*" to use
> copy_mc_enhanced_fast_string, this could work. I am not sure this is
> possible.

Yeah, no, this is for the copy to user direction only.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette