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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id 202sm18088610qkg.132.2020.03.06.16.34.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Mar 2020 16:34:19 -0800 (PST) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Subject: Re: [PATCH V15] mm/debug: Add tests validating architecture page table helpers Date: Fri, 6 Mar 2020 19:34:18 -0500 Message-Id: References: <61250cdc-f80b-2e50-5168-2ec67ec6f1e6@arm.com> Cc: linux-mm@kvack.org, Andrew Morton , Mike Rapoport , Vineet Gupta , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "Kirill A . Shutemov" , Paul Walmsley , Palmer Dabbelt , linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Christophe Leroy In-Reply-To: <61250cdc-f80b-2e50-5168-2ec67ec6f1e6@arm.com> To: Anshuman Khandual X-Mailer: iPhone Mail (17D50) 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 Mar 6, 2020, at 7:03 PM, Anshuman Khandual w= rote: >=20 > Hmm, set_pte_at() function is not preferred here for these tests. The idea= > is to avoid or atleast minimize TLB/cache flushes triggered from these sor= t > of 'static' tests. set_pte_at() is platform provided and could/might trigg= er > these flushes or some other platform specific synchronization stuff. Just Why is that important for this debugging option? > wondering is there specific reason with respect to the soft lock up proble= m > making it necessary to use set_pte_at() rather than a simple WRITE_ONCE() ?= Looks at the s390 version of set_pte_at(), it has this comment, vmaddr); /* * Certain architectures need to do special things when PTEs * within a page table are directly modified. Thus, the following * hook is made available. */ I can only guess that powerpc could be the same here.=