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[209.85.167.51]) by smtp.gmail.com with ESMTPSA id n25sm851768lfe.70.2019.03.10.17.22.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 10 Mar 2019 17:22:13 -0700 (PDT) Received: by mail-lf1-f51.google.com with SMTP id u2so2074769lfd.4 for ; Sun, 10 Mar 2019 17:22:12 -0700 (PDT) X-Received: by 2002:a19:700e:: with SMTP id h14mr15547896lfc.67.1552263732321; Sun, 10 Mar 2019 17:22:12 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Sun, 10 Mar 2019 17:21:56 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [GIT PULL] device-dax for 5.1: PMEM as RAM To: Dan Williams Cc: Linux Kernel Mailing List , linux-nvdimm , Linux MM , Dave Hansen , "Luck, Tony" Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Mar 10, 2019 at 4:54 PM Dan Williams wrote: > > Unfortunately this particular b0rkage is not constrained to nvmem. > I.e. there's nothing specific about nvmem requiring mc-safe memory > copy, it's a cpu problem consuming any poison regardless of > source-media-type with "rep; movs". So why is it sold and used for the nvdimm pmem driver? People told me it was a big deal and machines died. You can't suddenly change the story just because you want to expose it to user space. You can't have it both ways. Either nvdimms have more likelihood of, and problems with, machine checks, or it doesn't. The end result is the same: if intel believes the kernel needs to treat nvdimms specially, then we're sure as hell not exposing those snowflakes to user space. And if intel *doesn't* believe that, then we're removing the mcsafe_* functions. There's no "oh, it's safe to show to user space, but the kernel is magical" middle ground here that makes sense to me. Linus