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Tue, 31 Mar 2026 23:57:32 +0000 Date: Tue, 31 Mar 2026 16:57:26 -0700 From: Alison Schofield To: Li Ming CC: Davidlohr Bueso , Jonathan Cameron , Dave Jiang , "Vishal Verma" , Ira Weiny , "Dan Williams" , , Subject: Re: [PATCH] cxl/region: Add a region sysfs interface for region lock status Message-ID: References: <20260329-expose_region_locked_status-v1-1-cd860feaff6e@zohomail.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260329-expose_region_locked_status-v1-1-cd860feaff6e@zohomail.com> X-ClientProxiedBy: SJ0PR03CA0215.namprd03.prod.outlook.com (2603:10b6:a03:39f::10) To DS4PPF0BAC23327.namprd11.prod.outlook.com (2603:10b6:f:fc02::9) 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: DS4PPF0BAC23327:EE_|PH0PR11MB5093:EE_ X-MS-Office365-Filtering-Correlation-Id: 4514ef2a-70d1-4c99-30e0-08de8f81462f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024|56012099003|22082099003|18002099003; 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CXL region driver returns -EPERM for > region destroy operations. > There is at least 3 paths to a locked region: 1) the FIXED root decoder attribute (above) 2) CXL_HDM_DECODER0_CTRL_LOCK Both 1) and 2) well described in: 2230c4bdc412 ("cxl: Add handling of locked CXL decoder") 3) AMD Zen5 region creation always locks the region, regardless of the FIXED attribute or decoder ctrl bit. I like the added info provided by this patch. Please consider expanding the sysfs 'Decription:' field. If user reads the decoder lock sysfs description they may think they can reset their way out of a region lock situation, and I don't think they can. more... > Although the locked status of the corresponding root decoder implies the > region is also locked, exposing the region lock status directly to > userspace improves usability for users who may not be aware of this > relationship. > > Signed-off-by: Li Ming > --- > Documentation/ABI/testing/sysfs-bus-cxl | 10 ++++++++++ > drivers/cxl/core/region.c | 17 +++++++++++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl > index c80a1b5a03db..50bf7334465b 100644 > --- a/Documentation/ABI/testing/sysfs-bus-cxl > +++ b/Documentation/ABI/testing/sysfs-bus-cxl > @@ -508,6 +508,16 @@ Description: > (RO) The size of extended linear cache, if there is an extended > linear cache. Otherwise the attribute will not be visible. > > + > +What: /sys/bus/cxl/devices/regionZ/locked > +Date: Mar, 2026 > +KernelVersion: v7.1 > +Contact: linux-cxl@vger.kernel.org > +Description: > + (RO) The lock status of the region, region destroy operations > + are not permitted if the region is locked. Maybe similar to the sys/bus/cxl/devices/decoderX.Y/locked, say: The CXL driver has the capability to lock a region based on a BIOS or platform dependent configuration. Regions created as locked are never permitted to be destroyed. Resets to participating decoders will not result in a region destroy and will not free the decoder resources. Maybe the last sentence is too much. > + > + > What: /sys/bus/cxl/devices/regionZ/mode > Date: January, 2023 > KernelVersion: v6.3 > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c > index 42874948b589..95d81816008e 100644 > --- a/drivers/cxl/core/region.c > +++ b/drivers/cxl/core/region.c > @@ -767,6 +767,22 @@ static ssize_t extended_linear_cache_size_show(struct device *dev, > } > static DEVICE_ATTR_RO(extended_linear_cache_size); > > +static ssize_t locked_show(struct device *dev, > + struct device_attribute *attr, > + char *buf) > +{ > + struct cxl_region *cxlr = to_cxl_region(dev); > + int rc; > + > + ACQUIRE(rwsem_read_intr, rwsem)(&cxl_rwsem.region); > + if ((rc = ACQUIRE_ERR(rwsem_read_intr, &rwsem))) > + return rc; > + > + rc = test_bit(CXL_REGION_F_LOCK, &cxlr->flags); > + return sysfs_emit(buf, "%d\n", rc); > +} > +static DEVICE_ATTR_RO(locked); > + > static struct attribute *cxl_region_attrs[] = { > &dev_attr_uuid.attr, > &dev_attr_commit.attr, > @@ -776,6 +792,7 @@ static struct attribute *cxl_region_attrs[] = { > &dev_attr_size.attr, > &dev_attr_mode.attr, > &dev_attr_extended_linear_cache_size.attr, > + &dev_attr_locked.attr, > NULL, > }; > > > --- > base-commit: c369299895a591d96745d6492d4888259b004a9e > change-id: 20260329-expose_region_locked_status-b05c4b8f97d6 > > Best regards, > -- > Li Ming >