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[80.32.100.150]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-486eb32e81asm28641670f8f.7.2026.09.14.07.00.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Sep 2026 07:00:42 -0700 (PDT) Message-ID: <73837a51-e163-4b4e-8be2-4cdc044393b8@kernel.dk> Date: Mon, 14 Sep 2026 08:00:41 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 04/15] x86: implement thread identity handoff To: Peter Zijlstra Cc: io-uring@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@kernel.org, mingo@redhat.com References: <20260911154148.644489-1-axboe@kernel.dk> <20260911154148.644489-5-axboe@kernel.dk> <20260914114656.GC3500130@noisy.programming.kicks-ass.net> Content-Language: en-US From: Jens Axboe In-Reply-To: <20260914114656.GC3500130@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260914_070046_606421_84E9B7B6 X-CRM114-Status: GOOD ( 13.23 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 9/14/26 5:46 AM, Peter Zijlstra wrote: > On Fri, Sep 11, 2026 at 09:40:54AM -0600, Jens Axboe wrote: > >> +/* state bound to the task that neither side may have */ >> +static bool thread_handoff_task_ok(struct task_struct *tsk) >> +{ >> + /* I/O permissions, the bitmap hangs off the task */ >> + if (test_tsk_thread_flag(tsk, TIF_IO_BITMAP) || tsk->thread.iopl_emul) >> + return false; >> +#ifdef CONFIG_X86_USER_SHADOW_STACK >> + /* the shadow stack is per-thread and would have to move along */ >> + if (tsk->thread.features & ARCH_SHSTK_SHSTK) >> + return false; >> +#endif > > Distributions are having this enabled, this means nobody will pass this > check. Ah good point, should be feasible just by swapping s->shstk, s->features, and s->features_locked. Traveling right now, but I'll test that for the next version. -- Jens Axboe