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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id d16sm4004982qte.19.2020.09.09.11.03.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Sep 2020 11:03:25 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kG4RI-003r3t-JU; Wed, 09 Sep 2020 15:03:24 -0300 Date: Wed, 9 Sep 2020 15:03:24 -0300 From: Jason Gunthorpe To: Gerald Schaefer Cc: Dave Hansen , John Hubbard , LKML , linux-mm , linux-arch , Andrew Morton , Linus Torvalds , Russell King , Mike Rapoport , Catalin Marinas , Will Deacon , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Jeff Dike , Richard Weinberger , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Arnd Bergmann , Andrey Ryabinin , linux-x86 , linux-arm , linux-power , linux-sparc , linux-um , linux-s390 , Alexander Gordeev , Vasily Gorbik , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda Subject: Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table folding Message-ID: <20200909180324.GI87483@ziepe.ca> References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> <20200907180058.64880-2-gerald.schaefer@linux.ibm.com> <0dbc6ec8-45ea-0853-4856-2bc1e661a5a5@intel.com> <20200909142904.00b72921@thinkpad> <20200909192534.442f8984@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200909192534.442f8984@thinkpad> X-Rspamd-Queue-Id: 404121803F9B2 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 Wed, Sep 09, 2020 at 07:25:34PM +0200, Gerald Schaefer wrote: > I actually had to draw myself a picture to get some hold of > this, or rather a walk-through with a certain pud-crossing > range in a folded 3-level scenario. Not sure if I would have > understood my explanation above w/o that, but I hope you can > make some sense out of it. Or draw yourself a picture :-) What I don't understand is how does anything work with S390 today? If the fix is only to change pxx_addr_end() then than generic code like mm/pagewalk.c will iterate over a *different list* of page table entries. It's choice of entries to look at is entirely driven by pxx_addr_end(). Which suggest to me that mm/pagewalk.c also doesn't work properly today on S390 and this issue is not really about stack variables? Fundamentally if pXX_offset() and pXX_addr_end() must be consistent together, if pXX_offset() is folded then pXX_addr_end() must cause a single iteration of that level. Jason