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Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Frederic Weisbecker , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Jason Baron , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Juri Lelli , Marcelo Tosatti , Yair Podemsky , Daniel Wagner , Petr Tesarik Subject: Re: [RFC PATCH v3 06/15] jump_label: Add forceful jump label type Message-ID: <20241120145649.GJ19989@noisy.programming.kicks-ass.net> References: <20241119153502.41361-1-vschneid@redhat.com> <20241119153502.41361-7-vschneid@redhat.com> <20241119233902.kierxzg2aywpevqx@jpoimboe> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241119233902.kierxzg2aywpevqx@jpoimboe> X-Stat-Signature: eeykur6nsm98gi93ho64jkqataqg9bzw X-Rspam-User: X-Rspamd-Queue-Id: 270CA140003 X-Rspamd-Server: rspam02 X-HE-Tag: 1732114601-557389 X-HE-Meta: U2FsdGVkX18Lk6L/yFB461aZClOW20O0hsV5TKBrWgLCIxmLfkDZnLUwFuC+d46Ag1r/PERbLBvQP4lyVDrL+QTN2lrGC8RQFPbf+I1tTV0WXVuRKKLUMyNfBns8wDMiHgMPlYmMkocAAmBNGnSYQXWKwEhH84ok8p8M1LDPBwXnA68bkRYrOtvH8YHoHltlTjUUyCno/d9x3ZhBpXbtbRqdy1d7ho9xZ1MsEuSbn+iSczKPXObRYFskIti40rbMeEncFwGA2EfAaVKS0Qlks7CcZ98fsWSA2TzUlH2sPi4lu5zxca0AWOxTVtrI/fE7zQxqCKwGvMJVfXWYBHIRHJ6wITjkoQLBGxiuqZYic1u2aUcFaTphmUMHZuI1eDBzrHxtKi15qAuIh5BsejYSW6yTNIhHVAuTAJKAXwqZwQg7XTnowcWWw8zRCrNGRFTwAu1grM6AlmLuqD9shkPnVtcq4f3jo1XFCLhImy9ZwoMKqRjQD5ixU1Ac5TjEHkYJi5Oerc24YjY4prhNlXUAeP56YBd1nNABATeV4JQtiCj8GKT2SsDmXqrtcdOqgsRWS4Dz1rOuSoiwjHlQQ2aHWA4NZ0NEx3KssKPW3s4juxGpfEVsq0oNyt6HYuq7YlMKkpnA4PQ7uYJmnFQMwQ+0VZVv7I8U3hEyIeDa6txwbJwJTEwMzseLfqQHrx0K+23iRxbgYHv3F/a4YZGGRoSklAXqJudLXjsVUYUFvJIC5f/OFlY3TcyrWwBuz4UUlRIUXJl/EJbfOo8kzS5vRxnzCaDpbBvY6lvaSbGXMqGNfPc+2T4sT9qxhvj7gaB+rhsv+sizE8EKq08eW+UFwSq1/VTMBVkj8PmzigKbB3SY26UCsl/Apf/1LMyhuxuNqePhOwKEm/ht6m5AAjJF5tPCY+UdqFPeTc5/b1Nigi71ZpXEBZmsqzgMBmjGcF/AnNVlqJQRVWEVq+rgvPTjSp3 vV42CCyo Rr/QUtSUyLyumXictd1W6+dUxc+ItFwjmorusMR+EpM1fiF2gABA4k3Nl89WLRRPUGdI3T0zSBeZMln+kRnfEt8iaQdfgz9QbFE271/5/tWi/VgfshZCaxlyutUoFRiNLjV/efqBTZ0n1WzF65BrSbgOWuqNtmCE0oZpqNsz0BAjQcyHLXQV3C1qrdpZJ3/bYEhvaqKcGH/OwkJ32tuyo049tpEi9PliTEhkXpPnCqJtXjMhR/gQT7sfn5bVyXmyDnbUnCs/1cuEVEuc0DRGzFwqJrkaP0xJ0DEzHF6legbrU/1i3GITS+nPJaw== 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 Tue, Nov 19, 2024 at 03:39:02PM -0800, Josh Poimboeuf wrote: > On Tue, Nov 19, 2024 at 04:34:53PM +0100, Valentin Schneider wrote: > > Later commits will cause objtool to warn about non __ro_after_init static > > keys being used in .noinstr sections in order to safely defer instruction > > patching IPIs targeted at NOHZ_FULL CPUs. > > Don't we need similar checking for static calls? > > > Two such keys currently exist: mds_idle_clear and __sched_clock_stable, > > which can both be modified at runtime. > > Not sure if feasible, but it sure would be a lot simpler to just make > "no noinstr patching" a hard rule and then convert the above keys (or at > least their noinstr-specific usage) to regular branches. That'll be a bit of a mess. Also, then we're adding overhead/cost for all people for the benefit of this fringe case (NOHZ_FULL). Not a desirable trade-off IMO. So I do think the proposed solution (+- naming, I like your naming proposal better) is the better one. But I think we can make the fall-back safer, we can simply force the IPI when we poke at noinstr code -- then NOHZ_FULL gets to keep the pieces, but at least we don't violate any correctness constraints.