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Peter Anvin" , Nathan Chancellor , Nick Desaulniers , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, kernel-janitors@vger.kernel.org, linux-safety@lists.elisa.tech Subject: Re: [PATCH -next for tip:x86/pti] x86/tlb: drop unneeded local vars in enable_l1d_flush_for_task() In-Reply-To: <87eemji887.fsf@nanos.tec.linutronix.de> Message-ID: References: <20200928124457.27289-1-lukas.bulwahn@gmail.com> <20200929071211.GJ2628@hirez.programming.kicks-ass.net> <20200929083709.GC2651@hirez.programming.kicks-ass.net> <87eemji887.fsf@nanos.tec.linutronix.de> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Sep 2020, Thomas Gleixner wrote: > On Tue, Sep 29 2020 at 10:37, Peter Zijlstra wrote: > > Here, I fixed it.. > > Well, no. What Balbir is trying to do here is to establish whether a > task runs on a !SMT core. sched_smt_active() is system wide, but their > setup is to have a bunch of SMT enabled cores and cores where SMT is off > because the sibling is offlined. They affine these processes to non SMT > cores and the check there validates that before it enabled that flush > thingy. > > Of course this is best effort voodoo because if all CPUs in the mask are > offlined then the task is moved to a SMT enabled one where L1D flush is > useless. Though offlining their workhorse CPUs is probably not the daily > business for obvious raisins. > Thanks, Thomas. So, I will keep the semantics as-is, clean up the patch with preempt_{dis,en}able() and send out a v2. Lukas