Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20201207225703.2033611-1-ira.weiny@intel.com> <20201207225703.2033611-3-ira.weiny@intel.com>
 <20201207232649.GD7338@casper.infradead.org> <CAPcyv4hkY-9V5Rq5s=BRku2AeWYtgs9DuVXnhdEkara2NiN9Tg@mail.gmail.com>
 <20201207234008.GE7338@casper.infradead.org> <CAPcyv4g+NvdFO-Coe36mGqmp5v3ZtRCGziEoxsxLKmj5vPx7kA@mail.gmail.com>
 <20201208213255.GO1563847@iweiny-DESK2.sc.intel.com> <20201208215028.GK7338@casper.infradead.org>
 <CAPcyv4irF7YoEjOZ1iOrPPJDsw_-j4kiaqz_6Gf=cz1y3RpdoQ@mail.gmail.com>
 <20201208223234.GL7338@casper.infradead.org> <20201208224555.GA605321@magnolia>
In-Reply-To: <20201208224555.GA605321@magnolia>
From:   Dan Williams <dan.j.williams@intel.com>
Date:   Tue, 8 Dec 2020 15:40:52 -0800
Message-ID: <CAPcyv4jEmdfAz8foEUtDw4GEm2-+7J-4GULZ=6tCD+9K5CFzRw@mail.gmail.com>
Subject: Re: [PATCH V2 2/2] mm/highmem: Lift memcpy_[to|from]_page to core
To:     "Darrick J. Wong" <darrick.wong@oracle.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Eric Biggers <ebiggers@kernel.org>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, Dec 8, 2020 at 2:49 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
[..]
> > So what's your preferred poison?
> >
> > 1. Corrupt random data in whatever's been mapped into the next page (which
> >    is what the helpers currently do)
>
> Please no.

My assertion is that the kernel can't know it's corruption, it can
only know that the driver is abusing the API. So over-copy and WARN
seems better than violently regress by crashing what might have been
working silently before.