From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 73AB53F4102; Thu, 16 Jul 2026 08:56:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784192202; cv=none; b=ZBxdj/XDbHfmJDHhok5POFXEKY/Auatom34L/xMFhN1TyqOKSmbtCUY2xomrxcoPJeCddcbdjZBJhY29f0+DGsJAw47Rpstppccz7rnVCPaZB8jZHwF4cr92Th/fP/A/H+6vI51k7ZPxN3NSqW0o7PYIuPwBMTmq6KFZobRnn8Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784192202; c=relaxed/simple; bh=SmKu1jnHyjG0v36JD433LcEg5Si+tsyP9iuavPnkbjU=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=FjCZEkguxuDNWO5cNuXbY8pet+Ya6v/SGNUJ0npzVgkruVLpSmdfzrhVaq2J1Kpm3afUSDGLQfBT3iXqzXfUBqgOTe738xMJmuuB7brVpX/fuVi9ypz9/clG6BsiTQe0cTV0/27MbfRJdfcXH/VkRZ5hK/vTf3QyrEtSvi7jg54= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MDvErm+S; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MDvErm+S" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1F071F00A3E; Thu, 16 Jul 2026 08:56:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784192197; bh=gfnFMUC4iWdWRiNoNKCjBwV+rYNvS5DSxgAZrvVUf4A=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=MDvErm+SY2KmM+yxNcU9Ie+YMrEYjg0OnXNnu/5Q/KNgZ8jo1FMUZErwf6VURpmNb MJDpbOT9G2EEj+xR1/Y11LM2rjsIHWL4rT7lGugSa6wEEg37HXmU3tfR2yugib+zhm /mYhLifzXQEDaX9B+2WFfwHvhpJnrU7Dgxf/KVqiPk9qvsXEsvFR8Ny0WX7ysA/8S8 uFSbVJVTY6HdmIjcuKjy6AsV8spvaAIewOgIYxYp7P+cRSy22je8vqYXwEoq0SaF8s vNiHSNqE5vH40brx3uxfvJbIJ/5gSMPp85+hlo8ydOHBDEqtpFvqbh7KmTkFamvs2U 5CNUPIEhFz03w== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wkHtS-00000005bYF-1itT; Thu, 16 Jul 2026 08:56:34 +0000 Date: Thu, 16 Jul 2026 09:56:33 +0100 Message-ID: <867bmvnwhq.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton Cc: Wei-Lin Chang , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Itaru Kitayama , Sebastian Ene Subject: Re: [PATCH v4 3/6] KVM: arm64: nv: Add nested revmap broken tracepoint In-Reply-To: References: <20260714115926.2044757-1-weilin.chang@arm.com> <20260714115926.2044757-4-weilin.chang@arm.com> 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: oupton@kernel.org, weilin.chang@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, tabba@google.com, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, itaru.kitayama@fujitsu.com, sebastianene@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Thu, 16 Jul 2026 07:45:05 +0100, Oliver Upton wrote: > > Hi Wei-Lin, > > On Tue, Jul 14, 2026 at 12:59:22PM +0100, Wei-Lin Chang wrote: > > Add a tracepoint to track when a nested reverse map becomes broken. This > > makes it easier to detect NV performance degradation caused by full > > shadow stage-2 unmaps. > > > > Signed-off-by: Wei-Lin Chang > > I'm not too excited about making a tracepoint out of this, especially > since a 'broken' reverse map is more of a KVM implementation detail > (that could change) than anything else. > > BPF is quite popular at this point, do you think it's reasonable to > instead expect the curious KVM developer to attach a kprobe and inspect > the state of the nested MMU? I was the one asking for a way to report this stuff. I'd be completely fine with BPF as long as we give the recipe for this so that people can readily look at this. Even better, find a way not to have a broken rmap the first place ;-). Thanks, M. -- Without deviation from the norm, progress is not possible.