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[79.242.62.72]) by smtp.gmail.com with ESMTPSA id n68sm19504842wmn.13.2021.09.20.04.13.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Sep 2021 04:13:33 -0700 (PDT) Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases) To: Christoph Hellwig , Mike Rapoport Cc: Catalin Marinas , Robin Murphy , Alex Bee , Will Deacon , Andrew Morton , Anshuman Khandual , Linux Kernel Mailing List , linux-mm@kvack.org, Linux ARM References: <20210824173741.GC623@arm.com> <0908ce39-7e30-91fa-68ef-11620f9596ae@arm.com> <60a11eba-2910-3b5f-ef96-97d4556c1596@redhat.com> <20210825102044.GA3420@arm.com> <20210918051843.GA16104@lst.de> From: David Hildenbrand Organization: Red Hat Message-ID: <71b7d1b5-4a5f-9053-b22b-4d946cbf6d6e@redhat.com> Date: Mon, 20 Sep 2021 13:13:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210918051843.GA16104@lst.de> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AD30910000AE X-Stat-Signature: pnnfkgj1e513sfxqsuisd4gkkqan9zxm Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ApwcfJ4w; spf=none (imf07.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1632136417-434231 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 18.09.21 07:18, Christoph Hellwig wrote: > On Sat, Sep 18, 2021 at 12:22:47AM +0300, Mike Rapoport wrote: >> I did some digging and it seems that the most "generic" way to check if a >> page is in RAM is page_is_ram(). It's not 100% bullet proof as it'll give >> false negatives for architectures that do not register "System RAM", but >> those are not using dma_map_resource() anyway and, apparently, never would. > > The downside of page_is_ram is that it looks really expensiv for > something done at dma mapping time. > There would be ways to speed it up, similar to https://lkml.kernel.org/r/20210902160919.25683-2-david@redhat.com but the end result is still walking a list. Question would be, how much that overhead matters in practice. -- Thanks, David / dhildenb