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Message-ID: <78d4164c-adef-cedc-fb83-803150f64d11@suse.com> Date: Tue, 6 Dec 2022 12:05:25 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH 1/8] x86/mm: Avoid hard-coding PAT in get_page_from_l1e() Content-Language: en-US To: Demi Marie Obenour Cc: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= , Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , George Dunlap , Tim Deegan , xen-devel@lists.xenproject.org References: From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR3P281CA0017.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:1d::20) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|PA4PR04MB9247:EE_ X-MS-Office365-Filtering-Correlation-Id: 1881acdd-5d80-4af7-93a4-08dad779c7b4 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Removing this assumption would require a more complex > patch. > > Signed-off-by: Demi Marie Obenour You eliminate some assumptions at the price of introducing new ones. With that I consider the description insufficient; really there isn't any description here, just a statement on something you do _not_ do. > --- a/xen/arch/x86/mm.c > +++ b/xen/arch/x86/mm.c > @@ -961,13 +961,10 @@ get_page_from_l1e( > > switch ( l1f & PAGE_CACHE_ATTRS ) > { > - case 0: /* WB */ > - flip |= _PAGE_PWT | _PAGE_PCD; > - break; > - case _PAGE_PWT: /* WT */ > - case _PAGE_PWT | _PAGE_PAT: /* WP */ > - flip |= _PAGE_PCD | (l1f & _PAGE_PAT); > - break; > + case _PAGE_WB: > + case _PAGE_WT: > + case _PAGE_WP: > + flip |= (l1f & PAGE_CACHE_ATTRS) ^ _PAGE_UC; > } Please never drop "break" from case blocks, even if it's (at a given point in time) the last in its switch(). That's a recipe for someone else then forgetting to add it when another case block is added. Jan