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Message-ID: Date: Thu, 17 Nov 2022 14:33:16 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [PATCH] xen-pciback: Consider MSI-X enabled only when MASKALL bit is cleared Content-Language: en-US To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= Cc: linux-kernel@vger.kernel.org, Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , "moderated list:XEN HYPERVISOR INTERFACE" , David Vrabel References: <20221117114122.1588338-1-marmarek@invisiblethingslab.com> <0afe3f35-1b25-d1c6-89bb-8dae7a4070e9@cantab.net> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR0P281CA0059.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:49::7) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AM8PR04MB7971:EE_ X-MS-Office365-Filtering-Correlation-Id: 5d888d9b-49b7-4b55-6932-08dac8a0493b X-LD-Processed: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba,ExtFwd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Then it disables INTx just before clearing MASKALL >>> bit. Currently this approach is rejected by xen-pciback. >>> Allow setting PCI_MSIX_FLAGS_ENABLE while INTx is still enabled as long >>> as PCI_MSIX_FLAGS_MASKALL is set too. >> >> The use of MSI-X interrupts is conditional on only the MSI-X Enable bit. >> Setting MSI-X Enable effectively overrides the Interrupt Disable bit in the >> Command register. > > That means the second chunk of the patch may even drop the '(new_value & > PCI_MSIX_FLAGS_MASKALL)' part, right? > >> PCIe 6.0.1 section 7.7.2.2. "MSI-X Enable ... is prohibited from using INTx >> interrupts (if implemented)." And there is similar wording for MSI Enable. > > And this would mean the 'field_config->int_type == INTERRUPT_TYPE_MSIX' > part isn't necessary either. > > Jan in another thread pointed out that disabling INTx explicitly is > still a useful workaround for a flawed hardware. But if that isn't > mandated by the spec, maybe it doesn't need to be enforced by pciback > either? Well, allowing a device to go into a mode exhibiting undefined behavior is what we ought to prevent when it comes to a DomU doing so vs overall host safety. Jan