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Sun, 30 Nov 2025 18:15:23 +0000 Date: Sun, 30 Nov 2025 18:15:22 +0000 Message-ID: <878qfnfkud.wl-maz@kernel.org> From: Marc Zyngier To: Vincent Donnefort Cc: g@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, jstultz@google.com, qperret@google.com, will@kernel.org, aneesh.kumar@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 20/28] KVM: arm64: Add clock support for the pKVM hyp In-Reply-To: References: <20251107093840.3779150-1-vdonnefort@google.com> <20251107093840.3779150-21-vdonnefort@google.com> <86cy5erprc.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: vdonnefort@google.com, g@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, jstultz@google.com, qperret@google.com, will@kernel.org, aneesh.kumar@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org 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-20251130_101529_038475_20A0769C X-CRM114-Status: GOOD ( 23.10 ) 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 Thu, 20 Nov 2025 11:36:16 +0000, Vincent Donnefort wrote: > > [...] > > > > +/* Using host provided data. Do not use for anything else than debugging. */ > > > +u64 trace_clock(void) > > > +{ > > > + struct clock_data *clock = &trace_clock_data; > > > + u64 bank = smp_load_acquire(&clock->cur); > > > + u64 cyc, ns; > > > + > > > + cyc = __arch_counter_get_cntpct() - clock->data[bank].epoch_cyc; > > > > I can only imagine that you don't care about the broken systems that > > do not have a monotonic counter, and that will happily have their > > counter swing back and forth? > > I haven't used the _stable() variant for the affected devices... Hum this will > not be trivial from the hypervisor. I'll see what I can do. In all honestly, simply disabling tracing when you don't have a stable counter should be enough. I don't think there is much to be gained with supporting that on sub-standard HW (the bar is low enough). > > Also, you may want to document why you are using the physical counter > > instead of the virtual one. I guess that you don't want CNTVOFF_EL2 to > > apply when HCR_EL2.E2H==0, but given that you never allow anything > > else for pKVM, this is slightly odd. > > You mean I might as well use __arch_counter_get_cntvct() as CNTVOFF_EL2 will > always be ignored in the pKVM case? That, plus the fact that CNTVOFF_EL2 is only evaluated at EL2 when E2H=0 (and that case is going to disappear over time). M. -- Jazz isn't dead. It just smells funny.