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AJvYcCWG9REOjfOeRtFw9dCauPmskd9Lh0ee3OKmATzSorHeQU+IX5noe5iTVx4ug2Cv1lcTV1WXoM+pbg==@kvack.org X-Gm-Message-State: AOJu0YyWyVTu2zdo7UKu/Og1ciy4dzJQDvHeYWQEi1HOtNIiMHt6N20q uQy56SP9luiIzR5woLzyUYgDDQmgRzEMMMP+DX6R92qGeZNWeGmpJ4Xl/2Rfa0+W2GtUryEUHUk RBA== X-Google-Smtp-Source: AGHT+IFBt8EUJmCBrYJSR6SbgIXxnZj6fm10TNGjaAj4XRK+x0dRIzGirCE9VGAaKkDPtl0zEYTqCFRnILs= X-Received: from pfbcv2.prod.google.com ([2002:a05:6a00:44c2:b0:725:a760:4c72]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:148d:b0:725:eb85:f802 with SMTP id d2e1a72fcca58-72daf930e3cmr5815077b3a.2.1737134128872; Fri, 17 Jan 2025 09:15:28 -0800 (PST) Date: Fri, 17 Jan 2025 09:15:27 -0800 In-Reply-To: Mime-Version: 1.0 References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-26-vschneid@redhat.com> Message-ID: Subject: Re: [PATCH v4 25/30] context_tracking,x86: Defer kernel text patching IPIs From: Sean Christopherson To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, Peter Zijlstra , Nicolas Saenz Julienne , Juergen Gross , Ajay Kaher , Alexey Makhalov , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Kan Liang , Boris Ostrovsky , Josh Poimboeuf , Pawan Gupta , Paolo Bonzini , Andy Lutomirski , Arnd Bergmann , Frederic Weisbecker , "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 , Geert Uytterhoeven , Yosry Ahmed , "Kirill A. Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8FF7540003 X-Stat-Signature: dfyzkphf6qbpijkd8b15qfjs3g6s5qwy X-HE-Tag: 1737134130-153548 X-HE-Meta: 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 Qs+VCkps 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 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 Fri, Jan 17, 2025, Valentin Schneider wrote: > On 14/01/25 13:13, Sean Christopherson wrote: > > On Tue, Jan 14, 2025, Valentin Schneider wrote: > >> +/** > >> + * is_kernel_noinstr_text - checks if the pointer address is located in the > >> + * .noinstr section > >> + * > >> + * @addr: address to check > >> + * > >> + * Returns: true if the address is located in .noinstr, false otherwise. > >> + */ > >> +static inline bool is_kernel_noinstr_text(unsigned long addr) > >> +{ > >> + return addr >= (unsigned long)__noinstr_text_start && > >> + addr < (unsigned long)__noinstr_text_end; > >> +} > > > > This doesn't do the right thing for modules, which matters because KVM can be > > built as a module on x86, and because context tracking understands transitions > > to GUEST mode, i.e. CPUs that are running in a KVM guest will be treated as not > > being in the kernel, and thus will have IPIs deferred. If KVM uses a static key > > or branch between guest_state_enter_irqoff() and guest_state_exit_irqoff(), the > > patching code won't wait for CPUs to exit guest mode, i.e. KVM could theoretically > > use the wrong static path. > > AFAICT guest_state_{enter,exit}_irqoff() are only used in noinstr functions > and thus such a static key usage should at the very least be caught and > warned about by objtool - when this isn't built as a module. That doesn't magically do the right thing though. If KVM is built as a module, is_kernel_noinstr_text() will get false negatives even for static keys/branches that are annotaed as NOINSTR.