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Tue, 9 Jul 2024 19:13:50 +0000 Date: Tue, 9 Jul 2024 12:13:48 -0700 From: Dan Williams To: Yee Li , Christoph Hellwig , Dan Williams CC: Subject: Re: Is there any plan to support CXL GPF in Linux Message-ID: <668d8becca6cf_102cc294a3@dwillia2-xfh.jf.intel.com.notmuch> References: <668c877f86daf_102cc2941b@dwillia2-xfh.jf.intel.com.notmuch> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: MW4P223CA0024.NAMP223.PROD.OUTLOOK.COM (2603:10b6:303:80::29) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|SA1PR11MB6848:EE_ X-MS-Office365-Filtering-Correlation-Id: da061557-35e6-4007-3981-08dca04b4443 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?ukUjncblFNq3DM/qTU0eqIBuZZOFCtbuTJpZfS9QFK5Wdc10lkQZOOOvyFri?= =?us-ascii?Q?mDq8IyhGF1G582CppWMPQYiWIfWUd15BPtg/cBdx3UAlkCp8qOw913DND2HR?= =?us-ascii?Q?i4b7dwWScZ/Itl3mMzQBntRgaCycI80/v0uSnHZCxjGI8DWUT58OkEhDTCWR?= =?us-ascii?Q?d/2XZk4fQxHNAheDEAdJ0pRtDdWSJsB75d9PC1pmjdAZSpkVg+rKF5ay7Zxn?= =?us-ascii?Q?lHZOR6+Pl+TAprN0cVYJsSKqrXLgonttweRwpJcJg/vZNCShRI060wIsqoe5?= =?us-ascii?Q?dZotIB+kCyJw3gKuIHh3N+LGcMvnjDrwZLtg9vNAGVBsIgAh6WMp0evqG5k5?= =?us-ascii?Q?Y9fYrTEWEfic0cNISOehMb7YvzE4vIZlSy1qiHNZqtAY1bbX7NdGjl31Nxuf?= =?us-ascii?Q?EsHfEFejXl/rqyFB2fJVnJoGTdQx6UmujXq6bbIf5oLP0MRTDw5RnUvthjsn?= =?us-ascii?Q?nO3yXNyCu6NRIRhlz80Tp/J6xpFmMN6gc6MbkneFfoXCXpuCy+FRa6DU4RLq?= =?us-ascii?Q?z+ty9zDaLJtXnkUOM++Df92BELfSxxWznA86nk3Dfx5tpYsHGBfyuEW+mvHg?= =?us-ascii?Q?FMm7xT5jYhUHtYXWEzcYhyts2mBSjo2JddElBc37XnrFGwtvlZ/1YVcG3Mf8?= =?us-ascii?Q?JU97F91NgJkTe6vT9ROFOJVAAlnWg11JRa0d7b68U82CGGqodtyVV/SEX4rt?= =?us-ascii?Q?H4pbkQv2gtbfaVSpHlrdh8nCkWRD4cmEzamP3ri5oH0Yd2kg3QDLVCPhjEF9?= =?us-ascii?Q?gUn8YNgTd7Zottbd/n9dnqOHL0NStcZYMGiG5Lh2zgx+jO2cWuhWQOMOwsYP?= =?us-ascii?Q?mVcEz6x4PEl3mIlwHit+rbz4o1AbMz6E871y0B+UpiaWXBBF5HxOeZFpGEZA?= =?us-ascii?Q?/czM/UXMdEsjxDJEjYTuqdomLJyHAByBARd3sXtbWOtj6EDSenZaHx46fB5x?= =?us-ascii?Q?iU6KFFgXDV2QVSDf9iojGQtZ73kP21TfEJFbxZdHC0C8vSwvyUekAiJeq38n?= =?us-ascii?Q?saEYErnZ1JNqv/HDGil0Qnw+jqCMtrtdLqRt1C49k1BafkNdsjkTQSI47F8z?= =?us-ascii?Q?LApasZyRBXFC0pbO6lq0C+pl/X23vCGXWTNyPt3Nt4A6SfY5jruYH93G0ETP?= =?us-ascii?Q?S+FX53Vriu7d4m0iSmRRNLMPkh0P5iHYpzUJyq9HkI2AesksUgo0NPNL9K+w?= =?us-ascii?Q?sV89z+0P3X/LGGKaSD1d8rXH0HzMWdTuoGzR9+QA/yNnlzh00ZgErXXYCO62?= =?us-ascii?Q?t8eY1d/YZkHm4gOpZajZA1VHtF+8de794Fet1WhpnPdgiDHxU/QXtQPuJHJ0?= =?us-ascii?Q?ImA=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:PH8PR11MB8107.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(366016);DIR:OUT;SFP:1101; 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Or, support the flag and cap in the future. The Persistent CPU Caches flag is a performance optimization to avoid CPU cache flushing when the platform is trusted to take care of cache flushing at power-loss. Software can force "persistent caches" behavior by: echo 0 > /sys/block/pmem0/dax/write_cache >From a kernel developer perspective, I feel more comfortable with userspace making that "go fast at the risk of data-loss" decision. Maybe after the industry gets more experience with platforms that set that bit the kernel can default to trusting it, but given the slow roll out of CXL PMEM devices I think Linux is ok to take a "wait and see" attitude. At a minimum, if someone wants to draft a patch, it should be a build time configuration option to trust the FADT.