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Re: [PATCH v4 22/30] context_tracking: Exit CT_STATE_IDLE upon irq/nmi entry
- To: Frederic Weisbecker <frederic@xxxxxxxxxx>
- From: Valentin Schneider <vschneid@xxxxxxxxxx>
- Date: Mon, 10 Feb 2025 18:36:20 +0100
- Cc: linux-kernel@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, loongarch@xxxxxxxxxxxxxxx, linux-riscv@xxxxxxxxxxxxxxxxxxx, linux-perf-users@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, rcu@xxxxxxxxxxxxxxx, linux-hardening@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-kselftest@xxxxxxxxxxxxxxx, bpf@xxxxxxxxxxxxxxx, bcm-kernel-feedback-list@xxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>, Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>, Alexey Makhalov <alexey.amakhalov@xxxxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Huacai Chen <chenhuacai@xxxxxxxxxx>, WANG Xuerui <kernel@xxxxxxxxxx>, Paul Walmsley <paul.walmsley@xxxxxxxxxx>, Palmer Dabbelt <palmer@xxxxxxxxxxx>, Albert Ou <aou@xxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>, Namhyung Kim <namhyung@xxxxxxxxxx>, Mark Rutland <mark.rutland@xxxxxxx>, Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>, Jiri Olsa <jolsa@xxxxxxxxxx>, Ian Rogers <irogers@xxxxxxxxxx>, Adrian Hunter <adrian.hunter@xxxxxxxxx>, "Liang, Kan" <kan.liang@xxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, "Paul E. McKenney" <paulmck@xxxxxxxxxx>, Jason Baron <jbaron@xxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Ard Biesheuvel <ardb@xxxxxxxxxx>, Neeraj Upadhyay <neeraj.upadhyay@xxxxxxxxxx>, Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>, Josh Triplett <josh@xxxxxxxxxxxxxxxx>, Boqun Feng <boqun.feng@xxxxxxxxx>, Uladzislau Rezki <urezki@xxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>, Lai Jiangshan <jiangshanlai@xxxxxxxxx>, Zqiang <qiang.zhang1211@xxxxxxxxx>, Juri Lelli <juri.lelli@xxxxxxxxxx>, Clark Williams <williams@xxxxxxxxxx>, Yair Podemsky <ypodemsk@xxxxxxxxxx>, Tomas Glozar <tglozar@xxxxxxxxxx>, Vincent Guittot <vincent.guittot@xxxxxxxxxx>, Dietmar Eggemann <dietmar.eggemann@xxxxxxx>, Ben Segall <bsegall@xxxxxxxxxx>, Mel Gorman <mgorman@xxxxxxx>, Kees Cook <kees@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Shuah Khan <shuah@xxxxxxxxxx>, Sami Tolvanen <samitolvanen@xxxxxxxxxx>, Miguel Ojeda <ojeda@xxxxxxxxxx>, Alice Ryhl <aliceryhl@xxxxxxxxxx>, "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>, Samuel Holland <samuel.holland@xxxxxxxxxx>, Rong Xu <xur@xxxxxxxxxx>, Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>, Yosry Ahmed <yosryahmed@xxxxxxxxxx>, "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>, "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>, Jinghao Jia <jinghao7@xxxxxxxxxxxx>, Luis Chamberlain <mcgrof@xxxxxxxxxx>, Randy Dunlap <rdunlap@xxxxxxxxxxxxx>, Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
- Delivery-date: Mon, 10 Feb 2025 17:36:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07/02/25 19:37, Frederic Weisbecker wrote:
> Le Fri, Feb 07, 2025 at 06:06:45PM +0100, Valentin Schneider a écrit :
>>
>> Soooo I've been thinking...
>>
>> Isn't
>>
>> (context_tracking.state & CT_RCU_WATCHING)
>>
>> pretty much a proxy for knowing whether a CPU is executing in kernelspace,
>> including NMIs?
>
> You got it!
>
Yay!
>>
>> NMI interrupts userspace/VM/idle -> ct_nmi_enter() -> it becomes true
>> IRQ interrupts idle -> ct_irq_enter() -> it becomes true
>> IRQ interrupts userspace -> __ct_user_exit() -> it becomes true
>> IRQ interrupts VM -> __ct_user_exit() -> it becomes true
>>
>> IOW, if I gate setting deferred work by checking for this instead of
>> explicitely CT_STATE_KERNEL, "it should work" and prevent the
>> aforementioned issue? Or should I be out drinking instead? :-)
>
> Exactly it should work! Now that doesn't mean you can't go out
> for a drink :-)
>
Well, drinks were had very shortly after sending this email :D
> Thanks.
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