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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768383855; bh=iFG9jtDkQciBd3kw8laIsCgUzSrLhIKKl8rol2z2xpc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Lb8DXlDBnFqO+NW+Rh1u7EkBWHwkcRnCeq9olTQtKhAQ4m1b7rQKQulcGGmLgmiPg ANOxubQa8Qj1Lx4Uiq3ffkh9H+SgEQfPayen0wffEOzIOaFwOOPklamyu5uf9OZp2C mFsWPAryCARv4exsUjU8yE835fhhhvWyKBDOY1QGLxZvbTOUQM8ANwAroIonltUXJY FR1odw7cvxgh6UZZLFbiKglS4F778naUMuAQEPlENj8KARHm2sTb2cDh3QtKtrm22x Wo5WKPX5XSgVvnyLY9eHw1iI5yjfhv9A0JhupiXtYl1H6cqt+nhL0OXG1f7lScO91A oNlrXauO3pPsQ== Message-ID: Date: Wed, 14 Jan 2026 10:44:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 8/8] dax/kmem: add memory notifier to block external state changes To: Gregory Price , linux-mm@kvack.org Cc: linux-cxl@vger.kernel.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kernel-team@meta.com, dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, osalvador@suse.de, akpm@linux-foundation.org, Hannes Reinecke References: <20260114085201.3222597-1-gourry@gourry.net> <20260114085201.3222597-9-gourry@gourry.net> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 03D09C0004 X-Rspamd-Server: rspam06 X-Stat-Signature: siyp8xew6gzwtrzncyzrwi961uoc9z1b X-Rspam-User: X-HE-Tag: 1768383856-60197 X-HE-Meta: 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 5D3E4p1U yt+3qr+tRGHHpCqppLeUzYOSCyxS1sZxpiuU4wz4QLdxOjriOmo4lhrT+N7EHLq314/sKPgFZVsPg01b/xbRf0y2GA+tuKlW9aoTU12aJCBYMgA+Valkutq2psEl8W3JAfvXmAB47CCr8oQgC45A4ddiWT2p7kEwQo+tp+RrJdqfmYS9gaf/G7b+aCw+M5NmkCqdTiKpssMFU5fwlBVTftsU420QyY8J/ssL+gGzM21C0dxMQBfmVA7GpnQ9EV6VFoulH X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/14/26 09:52, Gregory Price wrote: > Add a memory notifier to prevent external operations from changing the > online/offline state of memory blocks managed by dax_kmem. This ensures > state changes only occur through the driver's hotplug sysfs interface, > providing consistent state tracking and preventing races with auto-online > policies or direct memory block sysfs manipulation. > > The notifier uses a transition protocol with memory barriers: > - Before initiating a state change, set target_state then in_transition > - Use a barrier to ensure target_state is visible before in_transition > - The notifier checks in_transition, then uses barrier before reading > target_state to ensure proper ordering on weakly-ordered architectures > > The notifier callback: > - Returns NOTIFY_DONE for non-overlapping memory (not our concern) > - Returns NOTIFY_BAD if in_transition is false (block external ops) > - Validates the memory event matches target_state (MEM_GOING_ONLINE > for online operations, MEM_GOING_OFFLINE for offline/unplug) > - Returns NOTIFY_OK only for driver-initiated operations with matching > target_state > > This prevents scenarios where: > - Auto-online policies re-online memory the driver is trying to offline Is this still a problem when using offline_and_remove_memory() ? > - Users manually change memory state via /sys/devices/system/memory/ I don't see why we would want to care about that :) > - Other kernel subsystems interfere with driver-managed memory state What do you have in mind? Not sure if this functionality here is really needed when the driver does add+online and offline+remove in a single operation. So please elaborate :) -- Cheers David