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Message-ID: Date: Thu, 2 Feb 2023 13:05:52 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 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@arm.com, wei.chen@arm.com, 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> From: Jan Beulich In-Reply-To: <20230202110816.1252419-8-luca.fancellu@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR3P281CA0113.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:a3::12) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|PA4PR04MB7616:EE_ X-MS-Office365-Filtering-Correlation-Id: 91c224a5-317e-42fb-a8be-08db0515d59c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Shall we create a struct arch for each > architecture and for example move arch_capabilities inside it (renaming to > capabilities) and every arch specific field as well? Counter question: Why don't you use (part of) arch_capabilities (and not just a single bit)? It looks to be entirely unused at present. Vector length being zero would sufficiently indicate absence of the feature without a separate boolean. > (is hw_cap only for x86?) I suppose it is, but I also expect it would better go away than be moved. It doesn't hold a complete set of information, and it has been superseded. Question is (and I think I did raise this before, perhaps in different context) whether Arm wouldn't want to follow x86 in how hardware as well as hypervisor derived / used ones are exposed to the tool stack (XEN_SYSCTL_get_cpu_featureset). I guess there's nothing really precluding that data to consist of more than just boolean fields. > --- 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. Jan