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Message-ID: <083e8a1f-8db6-350a-9138-58751c3fb44b@suse.com> Date: Mon, 13 Feb 2023 09:36:55 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH 07/10] xen/physinfo: add arm SVE arch capability and vector length Content-Language: en-US To: Luca Fancellu Cc: Bertrand Marquis , Wei Chen , Stefano Stabellini , Julien Grall , Volodymyr Babchuk , Andrew Cooper , George Dunlap , Wei Liu , "xen-devel@lists.xenproject.org" References: <20230202110816.1252419-1-luca.fancellu@arm.com> <20230202110816.1252419-8-luca.fancellu@arm.com> <781EDC8B-B24C-431F-AB08-F2ACF64E4D4E@arm.com> From: Jan Beulich In-Reply-To: <781EDC8B-B24C-431F-AB08-F2ACF64E4D4E@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR3P281CA0136.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:95::9) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AS8PR04MB8278:EE_ X-MS-Office365-Filtering-Correlation-Id: 9ba24c4e-6f70-498a-19a5-08db0d9d763b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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I guess there's nothing really precluding >> that data to consist of more than just boolean fields. > > Yes I guess that infrastructure could work, however I don’t have the bandwidth to > put it in place at the moment, so I would like the Arm maintainers to give me a > suggestion on how I can expose the vector length to XL if putting its value here > needs to be avoided Since you've got a reply from Andrew boiling down to the same suggestion (or should I even say request), I guess it wants seriously considering to introduce abstract base infrastructure first. As Andrew says, time not invested now will very likely mean yet more time to be invested later. >>> --- a/xen/include/public/sysctl.h >>> +++ b/xen/include/public/sysctl.h >>> @@ -18,7 +18,7 @@ >>> #include "domctl.h" >>> #include "physdev.h" >>> >>> -#define XEN_SYSCTL_INTERFACE_VERSION 0x00000015 >>> +#define XEN_SYSCTL_INTERFACE_VERSION 0x00000016 >> >> Why? You ... >> >>> @@ -104,7 +110,8 @@ struct xen_sysctl_physinfo { >>> uint32_t cpu_khz; >>> uint32_t capabilities;/* XEN_SYSCTL_PHYSCAP_??? */ >>> uint32_t arch_capabilities;/* XEN_SYSCTL_PHYSCAP_{X86,ARM,...}_??? */ >>> - uint32_t pad; >>> + uint16_t arm_sve_vl_bits; >>> + uint16_t pad; >>> uint64_aligned_t total_pages; >>> uint64_aligned_t free_pages; >>> uint64_aligned_t scrub_pages; >> >> ... add no new fields, and the only producer of the data zero-fills the >> struct first thing. > > Yes that is right, I will wait to understand how I can proceed here: > > 1) rename arch_capabilities to arm_sve_vl_bits and put vector length there. > 2) leave arch_capabilities untouched, no flag creation/setting, create uint32_t arm_sve_vl_bits field removing “pad”, > Use its value to determine if SVE is present or not. > 3) ?? 3) Introduce suitable #define(s) to use part of arch_capabilities for your purpose, without renaming the field. (But that's of course only if Arm maintainers agree with you on _not_ going the proper feature handling route right away.) Jan