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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <20230120175556.3556978-1-dhowells@redhat.com> <20230120175556.3556978-3-dhowells@redhat.com> To: Christoph Hellwig Cc: dhowells@redhat.com, Al Viro , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , John Hubbard , linux-mm@kvack.org Subject: Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3598254.1674307847.1@warthog.procyon.org.uk> Date: Sat, 21 Jan 2023 13:30:47 +0000 Message-ID: <3598255.1674307847@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: d5g8uubbj37gket6xx1jakxaagc3hoy1 X-Rspamd-Queue-Id: A3BBA180021 X-HE-Tag: 1674307857-735222 X-HE-Meta: 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 5g3QDkFa ByGajACpk2FTUuMsVvG3WVXiWgqdCGqVIqlhRxtoga0YzGxz4cKenSMK5yG1lw36X0wsdqE38otaU5oDl3Bmn4/pSYn8/MsLnh1jescw5GwknFvRJFYo+T57hRH8ekc/AmEUEb1r7x7ledu+IYpC9yR7Cg/vcDbrXG7zd73k/YCnsANf1Mn2HZIB4GwjGyWwzCD6XspoigAG95s1OF1bfYT80vsHWnNbxTEZt6FdNBVzzQ8upIbXKLCFTZqAoYg/mXeaTDOLm3blLu/4TOFEZbP3lCSD+b8FPcn8HyvJf7zoVkEhDkMveHVoaeSyIqAZRcuHl8Sph+Q5UO3eCPodQJvEFiyXRTEDT8VCB 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: Christoph Hellwig wrote: > On Fri, Jan 20, 2023 at 05:55:50PM +0000, David Howells wrote: > > (3) Any other sort of iterator. > > > > No refs or pins are obtained on the page, the assumption is made that > > the caller will manage page retention. ITER_ALLOW_P2PDMA is not > > permitted. > > The ITER_ALLOW_P2PDMA check here is fundamentally wrong and will > break things like io_uring to fixed buffers on NVMe. ITER_ALLOW_P2PDMA > should strictly increase the group of acceptable iters, it does must > not restrict anything. So just drop the check? Or do I actually need to do something to the pages to make it work? If I understand the code correctly, it's not actually operable right now on any page that doesn't have an appropriately marked PTE. David