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Mon, 20 Jan 2025 06:14:51 -0800 (PST) Message-ID: <2975f6a4-58ef-4499-b177-4b73ead4c670@gmail.com> Date: Mon, 20 Jan 2025 16:14:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 10/12] x86,tlb: do targeted broadcast flushing from tlbbatch code To: Rik van Riel , x86@kernel.org Cc: linux-kernel@vger.kernel.org, bp@alien8.de, peterz@infradead.org, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.com, thomas.lendacky@amd.com, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, jannh@google.com, mhklinux@outlook.com, andrew.cooper3@citrix.com References: <20250116023127.1531583-1-riel@surriel.com> <20250116023127.1531583-11-riel@surriel.com> <13bc0c49-09a4-434e-bd35-1ea50be38e25@gmail.com> <4dcf2b4ecaede883e2c7f6af3db58a4f6afaf4ad.camel@surriel.com> Content-Language: en-US From: Nadav Amit Autocrypt: addr=nadav.amit@gmail.com; keydata= xsFNBF3nSCQBEACinGNWCLb3Iptvg066zPUQCFfR0nIX+j/pjxlLd094zOKLJ7Z1wKNNTQgb +Y1GQYwKurK1hFHISPc1T7xk2twzov5niFqQp1/E0I6t/92rxo7C26tKMrCHgqXpFXXBaOvq t0QN8B83o3sfS3OZyc0F5hWoJijhKQ+h7dJHMPpBBeTWiZzYVlMNz/wRzYrh1nvesbGJtV1w Wk96qoQAOagczRaSRWouJ1O2JbHqQarLJG657hqtPZctQ1mkXQcJedT1c8ejWBdIiU0rIpV/ R2uTgM5NSjVrY5OxiS2G4C/bDcI4Q6ApWxqu1zRGffKWRFJdQvttSv+JbW2q6OCvJReJs1i6 nTovpfJb3g9d7U76LtAw7HE5iIl5CmyFoTMMH+sDc5PG7JRboiofku9DWeDGK4rB2s97GuA9 BXJDHBbH1AI+Y0H6oz/Dri1sQSayUU8Xj/jCkwxpwDle1qYYE0UM4PqDTUoeejURR/h/AREt bCecfxNUYNz2jY8PUL0YXj6yex2p1otMy5sy7djrTqhC02AXLQ3Oab2UJuMZnf4cTbN2sGXu CRXcCSsoyhxIFtwpgdVIDqkPMCOEPvUwy9hWs0N9Xy+jOebpH6FYxq83pP3IhyBdaoexoyGL IkSzrO4+0bVk5voh5SIYVkLEooMSEQT9rfSdrJmRRuM7S/PowwARAQABzSFOYWRhdiBBbWl0 IDxuYWRhdi5hbWl0QGdtYWlsLmNvbT7CwZcEEwEIAEECGwMFCwkIBwIGFQoJCAsCBBYCAwEC HgECF4ACGQEWIQRIkveiyXlibH/D0jUdoCpJptoPWgUCZWMLXAUJCz4qOAAKCRAdoCpJptoP WoWjD/0d8I+qQIHp2Eq7Whi+idkGDJaaBksRw2r0+XTzRj0CsCFJS7oMWudQaYaI2bTW9uha zfcmpnkm5aOVoxGOGJUJSy0H4of6lShE+7caoz1pdX+y15STij3+RvUjcGn0N+Mpxrnj6anm ArH5KOwzQJDiMF48ntQ2EQAFJ5X6YZ6Ed9N4I88XPeOtWaU21Q5tZI/ASHrQTH7BMukkVe2U PkSjn205vbrCfcC4Ohu9HXC8ey6l5txomFaTIRvaz1La3W8gQHhT2D2QeNnJFRudN5hQJNIE OHFi6QmPVIbI/uYD82h5uesiufycV2kvuIACmvs2T3tpaxSY9HOJF/yAhqg28hKE4wKQIwh2 wzZ+ywDeZ5TboqTjTU9oPHuRTxYItWmevJgQDwOYcssYI4wOdXvu/bh5VvhBgJxgkOOH7j8N efzqooL/2/pD/1JAO9GjPEWbuRx0dZh5tcMq/RYFFhdZQNFYmqdDyY0+y6ntxEo25ScvVLfR GqhpyJkN9+cqJZfg3IolbWoZxkSLtiCBge/EDRRoLJpjpsLpBmMmQcH/50WgQcoL5ObVlc1I ft1sKfzZvIyqXZfu3YcWgvOXfVXaMw1dXQ8ffwgyCSIsKvA5+Y45knd72SHny5z3gi1YsMc1 lm24v+OfxfmZMmJQ7TXBDl0JkOMnQ3A+KDb0oGAI6c7BTQRd50gkARAAt/NqfDSMph828JIn VOck27zsyT12AHRLIhsCCatw+zYbdMSLTW6hd/sChStdndAQlqOOW3mpm6bA+jl59c4OhkBW 8fDKgaWjVq8kBm4Z61zhzk3oXMmxgQ3cqMEfN36PCpcfs5MtLiMoa2JxaqFMQbKkmcZqz8fw qGIID/SMI5qdk+yWZSmR+6RdzXfppEIeqs78qTFxaEl+0MlAcgo2AjrMPLIjNK3k4jNAVCix KjMfkkPk6xVmP5Q7cr1st0xTTa1APt0y966oa6CZIdHY76D/jLpjJlfalctmEAxmyBqK0ZkK WDkEF+qCqqZ7oSkC1Q0ogBuBffIZb5srleqMz++IutiE4r/LELs7RanXXCRK5JYzZc/uAnxN fCJzqKR5/JxoSnCh0yQNU4FHa78DeD/SLnCu8JwTGkcX9ZUW/ZQ+5Nsimy+SlZb0UyaWA+vr Q7+F7OAL6PFsE8v+Q2u2EHwa8e2KmsL0sC+enBXbaogLFFfKi4I13vOk+76nCZTNetRhAubM etLe1PZZ0IDzgGhjFg+cc/jptq3qYjK+3jzhdKaqmoibAoea3E/5HsTVVbxUiYEdk2crTqf9 Mr5S5AzQfH19xU7uUduBvjN3L0dRKP0wJEqgCIB5gZBjD8AYmKSgdEujDAPQNXTJgwB99C+r F0XoHEmO6m9vI6djzDsAEQEAAcLBfAQYAQgAJgIbDBYhBEiS96LJeWJsf8PSNR2gKkmm2g9a BQJlYwtcBQkLPio4AAoJEB2gKkmm2g9ah7wP/jP18+dznONUt3Nga6XKYxxlVmVnMlqHx6SB jDWTwFzcQ6UeVVUmODWBSLI+iqg5djkgsTcHwI668qhIyyWaXC9ld+ONhUaE4NH1PKcJ8cdG vzhdTG8lM9mwmnJriTfih59OLI2yKpml/et44gvsfQpmFOyrdH9u6xPai5h3KyOoXD+Q3EzQ KEiHqs2x0PX72Jz4iVKEanP+qxEwzarUUcum94ecGilYY4jfxhfkgwBWjmC7ExbVTSEKIx3Q zdDbDiAxhAWymSisP3lbYqRo8mkg8r2emNan5L5Xh1b/62zmMO+p6gzucV7vO0VJxlKuUkFW 77Ug+X+hkDedvp2oRBz+wKtBxwSxlTM4toD49Jn111OMS6R5opquZP+/SJH1njSKY9MY3D3D 57QDpRUvqbqMDdqZqmYlMxntxTJ+0yksR61/t62F/bSp4XLxbgwCXMm73TxGrU73ngaS/Nxz Pv28VEcCGXZqFS2sbsbBSEjGgPhXf73YlI1fYiAFiaKHKvlofX+xNLeRHr9/+fL4JWPFurGi WYMyVA5Fv1sfefXhdEv9qNlhyNHxxB3vEpxkEOdo0JUhNfIcxe/w5iOfCUAtwUfvijvHUFHh U5QeQckJZTApjJ4S/Wa1ef8eS/LBsvG9xMNG3Ns+M+xR6unu6gTuzUNp7Zsxgmp8hs0racLB In-Reply-To: <4dcf2b4ecaede883e2c7f6af3db58a4f6afaf4ad.camel@surriel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9DED11A0010 X-Stat-Signature: e7ihot55ubmqjz96mgu8gp66fr1d87qb X-Rspam-User: X-HE-Tag: 1737382493-848582 X-HE-Meta: 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 /6kiV8S2 LQ62cwSUUogG5v/N2upE1onS8oaZG56WvxsBwuhNz7+9zqkimxFoEVLoGskucEF83VrX8k/Bvsw91SmanzTRjLWwJyMJBFYBbVMJBFJhIWsotWOK9gRqDJ9lY2674WfrmpEZJlltBHc/DBOM+FS2BFvd26TAGQfcF96KD3wlZyBSgvgM/F6il5PnqmQ48wIKGfMyTDb9ajpMsRQtjErNL6aTXa9IPDSROjXX8Tw23B6V4PMCexL0ttpkIxmLhXqCVATSvaBXaDx7SMmlA41dbN1qxV/eKQReK1SnLHObp4mjIBuxAs4S75eBTFiT4vc1/I93/8mWfRBwPq6ytWWp6HTt+NIZf9aOMROZvnLbEBF/gLcuHxiwyxhox50KpZkRbzR6pQ7klCY4GP/sM7BQqHnmf/hDt/kALb8ozfq9bC/hU+HZuOedG4imKzX+/FBl7cdFlKx452/vdUt4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.030466, 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 20/01/2025 16:02, Rik van Riel wrote: > On Mon, 2025-01-20 at 11:56 +0200, Nadav Amit wrote: >> >>> @@ -1670,12 +1668,62 @@ void arch_tlbbatch_flush(struct >>> arch_tlbflush_unmap_batch *batch) >>>    local_irq_enable(); >>>    } >>> >>> + /* >>> + * If we issued (asynchronous) INVLPGB flushes, wait for >>> them here. >>> + * The cpumask above contains only CPUs that were running >>> tasks >>> + * not using broadcast TLB flushing. >>> + */ >>> + if (cpu_feature_enabled(X86_FEATURE_INVLPGB) && batch- >>>> used_invlpgb) { >>> + tlbsync(); >>> + migrate_enable(); >> >> Maybe someone mentioned it before, but I would emphasize that I do >> not >> think that preventing migration for potentially long time is that >> great. >> >> One alternative solution would be to set a bit on cpu_tlbstate, that >> when set, you'd issue a tlbsync on context switch. >> >> (I can think about other solutions, but I think the one I just >> mentioned >> is the cleanest one). > > It is clean, but I'm not convinced it is good enough. > > We need to guarantee that the INVLPGBs have finished > before we free the pages. > > Running a TLBSYNC at the next context switch could > mean that TLBSYNC won't run until after the pages > have been freed. > > In practice it is probably good enough, since it > would be simpler for TLBSYNC to return once all > pending (older) INVLPGBs have finished, but it's > not architecturally guaranteed. > > We could send an IPI to remote CPUs in order for > them to call TLBSYNC, but is that really better? > I am not sure we are on the same page. What I suggested is: 1. arch_tlbbatch_flush() would still do tlbsync() 2. No migrate_enable() in arch_tlbbatch_flush() 3. No migrate_disable() in arch_tlbbatch_add_pending() 4. arch_tlbbatch_add_pending() sets cpu_tlbstate.pending_tlb_broadcast 5. switch_mm_irqs_off() checks cpu_tlbstate.pending_tlb_broadcast and if it is set performs tlbsync and clears it.