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Message-ID: Date: Thu, 4 Aug 2022 16:36:35 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v3 01/10] drivers/char: Add support for USB3 DbC debugger Content-Language: en-US To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= Cc: Andrew Cooper , George Dunlap , Julien Grall , Stefano Stabellini , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , xen-devel@lists.xenproject.org References: <3bd56b9d-023b-1991-90bf-bc44d3c75bc8@suse.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR3P281CA0087.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:1f::9) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 1b2f1786-7d0f-4659-69cc-08da7626bcc7 X-MS-TrafficTypeDiagnostic: AS4PR04MB9410:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Patch 8/10 is doing it. And >>> also, patch 8/10 is putting it together with other DMA-reachable >>> structures (not a separate page on its own). If I'd make it a separate >>> static variable (not part of that later struct), I'd need to reserve the >>> whole page for it - to guarantee no unrelated data lives on the same >>> (DMA-reachable) page. >>> >>> As for statically initializing it, if would require the whole >>> (multi-page DMA-reachable) thing living in .data, not .bss, so a bigger >>> binary (not a huge concern due to compression, but still). But more >>> importantly, I don't know how to do it in a readable way, and you have >>> complained about readability of initializer of this structure in v2. >>> >>>> That struct will be quite a bit less than a page's worth in size. >>> >>> See above - it cannot share page with unrelated Xen data. >> >> I have to admit that I'd see no issue if these lived side by side with >> e.g. other string literals. The more that the device is supposed to be >> exposed to Dom0 only anyway, and hence that'll be the only domain able >> to get at that data. > > Other string literals are fine. But for example `struct dbc` itself is > not. > See how it is combined with other data in patch 8. > >>>> If you build the file with -fshort-wchar, you may even be able to >>>> use easy to read string literals for the initializer. >>> >>> I can try, but I'm not exactly sure how to make readable UTF-16 >>> literals... >> >> L"Xen" looks sufficiently readable to me. We use this all over the >> place in the EFI interfacing code. > > Ok, I can try that. But given later adjustments, IIUC it will make the > whole 50+ pages structure land in .data. Is that okay? No. I was actually expecting the piece of data we're talking about here to land in .rodata, and hence be re-usable at the same address for all devices. Hence my reference to string literals. Jan