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[72.194.116.95]) by smtp.gmail.com with ESMTPSA id h14-20020a0cf44e000000b006263c531f61sm2508931qvm.24.2023.08.06.19.49.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 06 Aug 2023 19:49:01 -0700 (PDT) Message-ID: <39e96dd0-da7f-078e-d41d-fd437898744f@broadcom.com> Date: Sun, 6 Aug 2023 19:48:59 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] PCI: brcmstb: Avoid downstream access during link training To: =?UTF-8?Q?Pali_Roh=c3=a1r?= , Lukas Wunner Cc: Jim Quinlan , Nicolas Saenz Julienne , Lorenzo Pieralisi , Krzysztof Wilczynski , Rob Herring , Bjorn Helgaas , bcm-kernel-feedback-list@broadcom.com, linux-pci@vger.kernel.org, Philipp Rosenberger , Cyril Brulebois References: <385baf9dbfb6b65112803998dfc0cd6f84a5e6ba.1691296765.git.lukas@wunner.de> <20230806214338.7ylsi6aj6medp3us@pali> From: Florian Fainelli In-Reply-To: <20230806214338.7ylsi6aj6medp3us@pali> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="0000000000000b01b506024c4a3b" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org --0000000000000b01b506024c4a3b Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/6/2023 2:43 PM, Pali Rohár wrote: > On Sunday 06 August 2023 06:44:50 Lukas Wunner wrote: >> The Broadcom Set Top Box PCIe controller signals an Asynchronous SError >> Interrupt > > This is little incorrect wording. PCIe controller cannot send Async > SError, this is ARMv8 specific thing. In this case PCIe controller is > connected to ARM core via AXI bus and on PCIe transaction timeout it > sends AXI Slave Error, which then ARMv8 core reports to kernel as Async > SError interrupt. That is indeed a better way to explain the issue. FWIW, on BCM2711 the PCIe core connects via SCB and then AXI towards the ARMv8 CPU, does not change a thing about your paragraph. > > The proper fix is to configure PCIe controller to never send AXI Slave > Error and neither AXI Decode Error (to prevent SErrors at all). For > example Synopsys PCIe controllers have proprietary hidden configuration > bits for enabling/disabling this AXI error reporting behavior. That does not exist with the version of the block present in BCM2711 unfortunately. > > Or second option is to access affected memory from the ARMv8 core via > synchronous operations and map memory as nGnRnE. Then ARMv8 core reports > AXI Slave Error as Synchronous Abort Exception which you can catch, > examine that was caused on PCIe memory region and fabricate all-ones > response. But the second option is not available for some licensed ARMv8 > Cortex cores (e.g. A53) as they do not implement nE (non Early Write > Acknowledgement) memory mapping correctly. BCM2711 uses Cortex-A72 do these cores still not implement nE correctly? Do you have a reference backing up that claim (not disputing it, just curious). > > The patch below does not fix the issue at all, instead it opens a new > race condition that if link state is changed _after_ the check and > _before_ accessing config space. Fair enough, but in the situation you describe there is not much that can be done anyway so we might as well deal with a narrowed window? 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