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Peter Anvin" , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Boris Ostrovsky , Josh Poimboeuf , Pawan Gupta , Sean Christopherson , Paolo Bonzini , Andy Lutomirski , Arnd Bergmann , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juri Lelli , Clark Williams , Yair Podemsky , Tomas Glozar , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Andrew Morton , Christoph Hellwig , Shuah Khan , Sami Tolvanen , Miguel Ojeda , Alice Ryhl , "Mike Rapoport (Microsoft)" , Samuel Holland , Rong Xu , Nicolas Saenz Julienne , Geert Uytterhoeven , Yosry Ahmed , "Kirill A. Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Subject: Re: [PATCH v4 22/30] context_tracking: Exit CT_STATE_IDLE upon irq/nmi entry Message-ID: References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-23-vschneid@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250114175143.81438-23-vschneid@redhat.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1C1001A0006 X-Stat-Signature: ab9uatapze88nhw95x6merf9ota917ki X-Rspam-User: X-HE-Tag: 1737505336-511861 X-HE-Meta: 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 ORcjSuWB I3Ku10IgLIcBq9GzhiEThBNb8CAw3PcypsnGbkKkeBZ/TxVYzXA9fjJEHycoD/OZf9phxhWOEvTUz8nWBulV26axynDl48GJdK1vKQGus9ZIY47GZsXUVpLNeCx/b6Mc7hV+vuvwEeQp2E+7gyt1Gv5KjV3zBwIK+ZYsJfppGj7d4kNH2Ix4Usgs4tTSRXsW1ssyKJ053XMmwGwukPjzCxmVYhYzBPmNUUsKgN1rCTT0Vm4DE2p58+wKqT7WvrmnZzl+XD5xJ366NWC2a/rEGfwvvdtU4jOJZg8MC+YQj69cb6KGavCL26wLybc5dCqyJNeEYkBjiqEDAhz0bFrhkwao3R6WYPMEbd1Ci 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: Le Tue, Jan 14, 2025 at 06:51:35PM +0100, Valentin Schneider a écrit : > ct_nmi_{enter, exit}() only touches the RCU watching counter and doesn't > modify the actual CT state part context_tracking.state. This means that > upon receiving an IRQ when idle, the CT_STATE_IDLE->CT_STATE_KERNEL > transition only happens in ct_idle_exit(). > > One can note that ct_nmi_enter() can only ever be entered with the CT state > as either CT_STATE_KERNEL or CT_STATE_IDLE, as an IRQ/NMI happenning in the > CT_STATE_USER or CT_STATE_GUEST states will be routed down to ct_user_exit(). Are you sure? An NMI can fire between guest_state_enter_irqoff() and __svm_vcpu_run(). And NMIs interrupting userspace don't call enter_from_user_mode(). In fact they don't call irqentry_enter_from_user_mode() like regular IRQs but irqentry_nmi_enter() instead. Well that's for archs implementing common entry code, I can't speak for the others. Unifying the behaviour between user and idle such that the IRQs/NMIs exit the CT_STATE can be interesting but I fear this may not come for free. You would need to save the old state on IRQ/NMI entry and restore it on exit. Do we really need it? Thanks.