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Wed, 21 Jan 2026 08:38:17 +0000 Date: Wed, 21 Jan 2026 08:38:17 +0000 Message-ID: <861pjjcqdi.wl-maz@kernel.org> From: Marc Zyngier To: Waiman Long , Thomas Gleixner Cc: Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH] irqchip/gic-v3-its: Don't acquire rt_spin_lock in allocate_vpe_l1_table() In-Reply-To: <86tswrkrh4.wl-maz@kernel.org> References: <20260107215353.75612-1-longman@redhat.com> <864iowmrx6.wl-maz@kernel.org> <87ms2nsqju.ffs@tglx> <86wm1qlq7l.wl-maz@kernel.org> <87ecnwij44.ffs@tglx> <86v7h8l9ht.wl-maz@kernel.org> <87pl7gglya.ffs@tglx> <86tswrkrh4.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: longman@redhat.com, tglx@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260121_003822_872231_3EF9F475 X-CRM114-Status: GOOD ( 32.95 ) 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 Mon, 12 Jan 2026 11:20:07 +0000, Marc Zyngier wrote: > > On Sun, 11 Jan 2026 16:20:45 +0000, > Thomas Gleixner wrote: > > > > On Sun, Jan 11 2026 at 10:38, Marc Zyngier wrote: > > > On Sun, 11 Jan 2026 09:39:07 +0000, > > > Thomas Gleixner wrote: > > >> > > >> On Fri, Jan 09 2026 at 16:13, Marc Zyngier wrote: > > >> > On Thu, 08 Jan 2026 22:11:33 +0000, > > >> > Thomas Gleixner wrote: > > >> >> At the point where a CPU is brought up, the topology should be known > > >> >> already, which means this can be allocated on the control CPU _before_ > > >> >> the new CPU comes up, no? > > >> > > > >> > No. Each CPU finds *itself* in the forest of redistributors, and from > > >> > there tries to find whether it has some shared resource with a CPU > > >> > that has booted before it. That's because firmware is absolutely awful > > >> > and can't present a consistent view of the system. > > >> > > >> Groan.... > > >> > > >> > Anyway, I expect it could be solved by moving this part of the init to > > >> > an ONLINE HP callback. > > >> > > >> Which needs to be before CPUHP_AP_IRQ_AFFINITY_ONLINE, but even that > > >> might be to late because there are callbacks in the STARTING section, > > >> i.e. timer, perf, which might rely on interrupts being accessible. > > > > > > Nah. This stuff is only for direct injection of vLPIs into guests, so > > > as long as this is done before we can schedule a vcpu on this physical > > > CPU, we're good. No physical interrupt is concerned with this code. > > > > That's fine then. vCPUs are considered "user-space" tasks and can't be > > scheduled before CPUHP_AP_ACTIVE sets the CPU active for the scheduler. > > Waiman, can you please give the following hack a go on your box? The > machines I have are thankfully limited to a single ITS group, so I > can't directly reproduce your issue. Have you managed to try this hack? I may be able to spend some time addressing the issue in the next cycle if I have an indication that I'm on the right track. Thanks, M. -- Without deviation from the norm, progress is not possible.