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Peter Anvin" , "Rafael J. Wysocki" , Pavel Machek , Greg Kroah-Hartman , Danilo Krummrich , Johan Hovold , Sebastian Andrzej Siewior , Mathieu Desnoyers , Jiayuan Chen , "Steven Rostedt (Google)" , "Vineeth Pillai (Google)" , Frederic Weisbecker , Andi Kleen , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, driver-core@lists.linux.dev Subject: Re: [PATCH 2/6] perf/x86/intel/pt: Stop tracing if VMXON has not yet happened Message-ID: <20261102110752.GX1779021@noisy.programming.kicks-ass.net> References: <20261102074039.26983-1-adrian.hunter@intel.com> <20261102074039.26983-3-adrian.hunter@intel.com> <20261102095750.GS1779021@noisy.programming.kicks-ass.net> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Nov 02, 2026 at 01:04:59PM +0200, Adrian Hunter wrote: > > It seems rather unfortunate to issue a RDMSR for state we fully control. > > Surely we can track this? > > The RDMSR only happens on BDW and only when VMX is on and someone still > tries to use Intel PT (even though no trace can be produced on BDW > while VMX is on). > > There is a window between setting vmx_on and clearing TRACEEN. Dealing > with that would be complicated, compared with reading the MSR. So I thought we'd manually clear the thing before VMXON, but you're saying VMXON itself will clobber that register? I stand by my previous statement ;-)