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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id m17sm931967qkn.45.2020.08.28.07.21.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2020 07:21:37 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kBfG5-000hDT-3F; Fri, 28 Aug 2020 11:21:37 -0300 Date: Fri, 28 Aug 2020 11:21:37 -0300 From: Jason Gunthorpe To: Gerald Schaefer Cc: Linus Torvalds , Andrew Morton , linux-mm , LKML , Vasily Gorbik , Alexander Gordeev , linux-s390@vger.kernel.org, Heiko Carstens , Claudio Imbrenda , Christian Borntraeger Subject: Re: [RFC PATCH 0/2] mm/gup: fix gup_fast with dynamic page table folding Message-ID: <20200828142137.GX24045@ziepe.ca> References: <20200828140314.8556-1-gerald.schaefer@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200828140314.8556-1-gerald.schaefer@linux.ibm.com> X-Rspamd-Queue-Id: 004FA37604 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 28, 2020 at 04:03:12PM +0200, Gerald Schaefer wrote: > Commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast > code") introduced a subtle but severe bug on s390 with gup_fast, due to > dynamic page table folding. I think the page walk code in mm/pagewalk.c has similar issues to GUP. I've been noodling on some patches to add the missing stack copies to pagewalk.c as they are clearly missing.. It would be good if this could be less GUP specific? Generically this is about walking the page table without holding the page table spinlocks using READ_ONCE. Jason