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[209.85.208.174]) by smtp.gmail.com with ESMTPSA id z17sm5608422ljn.101.2020.04.12.09.33.54 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 12 Apr 2020 09:33:54 -0700 (PDT) Received: by mail-lj1-f174.google.com with SMTP id r24so6596680ljd.4 for ; Sun, 12 Apr 2020 09:33:54 -0700 (PDT) X-Received: by 2002:a2e:870f:: with SMTP id m15mr8469452lji.16.1586709234124; Sun, 12 Apr 2020 09:33:54 -0700 (PDT) MIME-Version: 1.0 References: <20200412004155.1a8f4e081b4e03ef5903abb5@linux-foundation.org> <20200412074250.0cE0EZy6-%akpm@linux-foundation.org> In-Reply-To: <20200412074250.0cE0EZy6-%akpm@linux-foundation.org> From: Linus Torvalds Date: Sun, 12 Apr 2020 09:33:38 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 1/1] mm/debug: add tests validating architecture page table helpers To: Andrew Morton Cc: anshuman.khandual@arm.com, Benjamin Herrenschmidt , Christian Borntraeger , Borislav Petkov , Qian Cai , Catalin Marinas , Christophe Leroy , Gerald Schaefer , Vasily Gorbik , Heiko Carstens , Peter Anvin , "Kirill A . Shutemov" , Linux-MM , Ingo Molnar , Ingo Molnar , mm-commits@vger.kernel.org, Michael Ellerman , Palmer Dabbelt , Paul Walmsley , Paul Mackerras , Mike Rapoport , Thomas Gleixner , vgupta@synopsys.com, Will Deacon Content-Type: text/plain; charset="UTF-8" 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 Sun, Apr 12, 2020 at 12:42 AM Andrew Morton wrote: > > 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 > inside kernel_init() right after async_synchronize_full(). This last part makes absolutely zero sense to me. Why would it be done before the machine is properly up? Why isn't this just a module with a module_init? What makes this test so important and magical that it has to be done during early boot? So not applied, particularly since this apparently caused problems. We don't randomly break the boot, which is fragile anyway, just for a test that doesn't look like it should be boot-specific to me. If it wants a new clean mm, it should just do a fork. And do so _looong_ long after boot. Linus