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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id m21sm11036189qka.117.2020.01.27.18.11.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jan 2020 18:11:54 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers Date: Mon, 27 Jan 2020 21:11:53 -0500 Message-Id: <14882A91-17DE-4ABD-ABF2-08E7CCEDF660@lca.pw> References: <1580174873-18117-1-git-send-email-anshuman.khandual@arm.com> Cc: linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Greg Kroah-Hartman , Thomas Gleixner , Mike Rapoport , Jason Gunthorpe , Dan Williams , Peter Zijlstra , Michal Hocko , Mark Rutland , Mark Brown , Steven Price , Ard Biesheuvel , Masahiro Yamada , Kees Cook , Tetsuo Handa , Matthew Wilcox , Sri Krishna chowdary , Dave Hansen , Russell King - ARM Linux , Michael Ellerman , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Vineet Gupta , James Hogan , Paul Burton , Ralf Baechle , "Kirill A . Shutemov" , Gerald Schaefer , Christophe Leroy , Ingo Molnar , linux-snps-arc@lists.infradead.org, linux-mips@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <1580174873-18117-1-git-send-email-anshuman.khandual@arm.com> To: Anshuman Khandual X-Mailer: iPhone Mail (17C54) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jan 27, 2020, at 8:28 PM, Anshuman Khandual = wrote: >=20 > This adds tests which will validate architecture page table helpers and > other accessors in their compliance with expected generic MM semantics. > This will help various architectures in validating changes to existing > page table helpers or addition of new ones. >=20 > This test covers basic page table entry transformations including but not > limited to old, young, dirty, clean, write, write protect etc at various > level along with populating intermediate entries with next page table page= > and validating them. >=20 > Test page table pages are allocated from system memory with required size > and alignments. The mapped pfns at page table levels are derived from a > real pfn representing a valid kernel text symbol. This test gets called > right after page_alloc_init_late(). >=20 > This gets build and run when CONFIG_DEBUG_VM_PGTABLE is selected along wit= h > CONFIG_VM_DEBUG. Architectures willing to subscribe this test also need to= > select CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE which for now is limited to x86 an= d > arm64. Going forward, other architectures too can enable this after fixing= > build or runtime problems (if any) with their page table helpers. What=E2=80=99s the value of this block of new code? It only supports x86 and= arm64 which are supposed to be good now. Did those tests ever find any regr= ession or this is almost only useful for new architectures which only happen= ed once in a few years? The worry if not many people will use this config an= d code those that much in the future because it is inefficient to find bugs,= it will simply be rotten like a few other debugging options out there we ha= ve in the mainline that will be a pain to remove later on.=