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Tue, 14 Jan 2025 12:32:29 +0000 (UTC) Date: Tue, 14 Jan 2025 13:32:28 +0100 From: Borislav Petkov To: Rik van Riel Cc: x86@kernel.org, linux-kernel@vger.kernel.org, peterz@infradead.org, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.com, nadav.amit@gmail.com, thomas.lendacky@amd.com, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, jannh@google.com Subject: Re: [PATCH v4 01/12] x86/mm: make MMU_GATHER_RCU_TABLE_FREE unconditional Message-ID: <20250114123228.GAZ4ZZXK7Vd-KlM-Cc@fat_crate.local> References: <20250112155453.1104139-1-riel@surriel.com> <20250112155453.1104139-2-riel@surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250112155453.1104139-2-riel@surriel.com> X-Stat-Signature: j5gp8tuxyzfprpfsj79ww1qemheegpi8 X-Rspamd-Queue-Id: 7AF181A0013 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1736857967-158749 X-HE-Meta: U2FsdGVkX19OlTxSEWeF+Bvdt1/IEE0ervz3A3hjDNWT6r645aaZnLNJHkstVOBQ7YkNtIaWz5sWTFh8JFMi4mEAvedYcuj449KgvrYANDzmkbqsjiKknz5dR2Hd1g6Vb6PDvzurXrrwiXN1Z5iU/867iwKpFNjZmQz4uKqRucxO2weABiylo6MyvRwdRX2GkHXInQ3Fipg3pHHlzyPg5ms4jmShHCpD/cq+NO514ZEAPt9Rgub1bb4/BNfuZluRL9L/IHb1nwagqsrp8X76ubUcfTQ2fJ9rPPazZGIqmgwP9T7dK565gL5rPKK3AHYsye1AggNVJd+Isii3eX/Zs4Vq/wsCbrpz+AVgWCfRukXTucF0RN6ZBJ+OmUNUvliuAsQUJSeCh3VFSPYIwfiyVQmHjsLw+EDUMOCOweR3Q7r1a3DTaEenCfyiI+RNaiYYXSsHPZffXdW1FUMIo6ZA2fWYfQzyTWH9iCbdnjv8sYdLEjedzbGs/TpzJpkmsmMfHmtIgjdpEsIrrRjyemNANrV6j2bTJPBtVqxJOMbJMqo1hFoDklTHsqOfS7zl90VfEki+MLd+k0khZD7tU6eCqoU1D3RmFruiuRcT/RXhl2VObslqa0lXxgLBL98H9V4BUDWQLCl6abf41G+AM6dr4xrYORApYzIY5ui2tdvPpRSoRKJIaFavBDFdG1UoQokxmDAQ4QMmGPwY5HCh4xc0ab1VsCq6Fx12p2DuS3xvHyVMRizyYA7nnE+mMmhuWVvlgqghb1GGvJuvpk8bP3d0N47So/8luVO2e1vOSB7fy51lL/jajS3eL7sXHq9kIs2ereg/e9CWv0ZBw7OL5u10ugAoJCfoA1DfrH6TJ3nEAKaqBgoKcJN0dS38X4tX6rV8PPXBqFXdVMsoI/yvyu5e+hfPqPZ36QJxF1UBKHF8Xcqyvh8LKges13HNxH+1d6nCT8GnTfHNGx6A/AQTtfI ZVWbaFVE KuHp2Ctl1OYzvtOrvgqsC8/HQWteQJDLHR6JaLmOnqw/SwwxvYeo82Sm3mDPuBIPUAogmEGaHBQSD4fU6Y/9S6QZWObXw5ZGpkj+1EKTo3A+lYZBAtPTL0mL4Ld0Ip+GaEpMgfUCEdYThFzOrsIaHd2uRtqg49Tc680PFj2yJMxlqO/Oh5Mss9BP7eM5jJ+bcnL4azUUxXlUYOBKWMYhRUBPaKY+lRRa7DDlJSEjf5wq5+H+qQdJfC0msUCVeIKpvRg4Tv85o5TlIiyC9PKfQ5vf9Q3ll1KJVCwL5tK0I9zdcOS4p+v2mW85a35oXBYQPmekmZUfzf7gosmqwBSYfgBOBBqHQHdK1xcfIlQGo28wmhjSbX1b5cfbH7A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 Sun, Jan 12, 2025 at 10:53:45AM -0500, Rik van Riel wrote: > Currently x86 uses CONFIG_MMU_GATHER_TABLE_FREE when using > paravirt, and not when running on bare metal. > > There is no real good reason to do things differently for > each setup. Make them all the same. > > Currently get_user_pages_fast synchronizes against page table > freeing in two different ways: > - on bare metal, by blocking IRQs, which block TLB flush IPIs > - on paravirt, with MMU_GATHER_RCU_TABLE_FREE > > This is done because some paravirt TLB flush implementations > handle the TLB flush in the hypervisor, and will do the flush > even when the target CPU has interrupts disabled. > > After this change, the synchronization between get_user_pages_fast get_user_pages_fast() - make it look like a function. Avoid having "This patch" or "This commit" or "After this change", etc in the commit message. It is tautologically useless so use imperative tone directly: "Always handle page table freeing with..." > and page table freeing is always handled with MMU_GATHER_RCU_TABLE_FREE, > which allows bare metal to also do TLB flushes while interrupts are > disabled. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette