From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-198.mta0.migadu.com (out-198.mta0.migadu.com [91.218.175.198]) (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 68D971B278 for ; Mon, 23 Oct 2023 18:25:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="iGsEJTbQ" Date: Mon, 23 Oct 2023 18:24:50 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1698085497; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QChXizP9EOxkwbrFQch52NiZrZiX3EIsRZVyKac4G8c=; b=iGsEJTbQ/pmMU0i2n2T//fvlwiheDsxmxNhjnWiFSsNvn4EPsecSVhGKbgbtV895dlfywq IFjdHTrBHuojcaQo0vPWHH9hRFTHd4Lqd1F5YmaOKrheubFebH5vabBSjt7EM/OUgS6urb MG1CLX6vy1Wu+Y/7MI/oyahdTxTzOPk= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Marc Zyngier Cc: Raghavendra Rao Ananta , Alexandru Elisei , James Morse , Suzuki K Poulose , Paolo Bonzini , Zenghui Yu , Shaoqin Huang , Jing Zhang , Reiji Watanabe , Colton Lewis , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v8 02/13] KVM: arm64: PMU: Set the default PMU for the guest before vCPU reset Message-ID: References: <20231020214053.2144305-1-rananta@google.com> <20231020214053.2144305-3-rananta@google.com> <8634y162q5.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8634y162q5.wl-maz@kernel.org> X-Migadu-Flow: FLOW_OUT On Mon, Oct 23, 2023 at 11:40:50AM +0100, Marc Zyngier wrote: [...] > > +static int kvm_setup_vcpu(struct kvm_vcpu *vcpu) > > +{ > > + struct kvm *kvm = vcpu->kvm; > > + > > + /* > > + * When the vCPU has a PMU, but no PMU is set for the guest > > + * yet, set the default one. > > + */ > > + if (kvm_vcpu_has_pmu(vcpu) && !kvm->arch.arm_pmu && > > + kvm_arm_set_default_pmu(kvm)) > > + return -EINVAL; > > nit: I'm not keen on re-interpreting the error code. If > kvm_arm_set_default_pmu() returns an error, we should return *that* > particular error, and not any other. Something like: The code took this shape because I had an issue with returning ENODEV on the KVM_ARM_VCPU_INIT ioctl, which is not a documented error code. Now that the vCPU flags are sanitised early in the ioctl, KVM has decided at this point that vPMU is a supported feature. Given that, I think ENODEV is fine now as the unexpected return value would indicate a bug in KVM. > Hmmm. Contrary to what the commit message says, the default PMU is not > picked at reset time, but at the point where the target is set (the > very first vcpu init). Which is pretty different from reset, which > happens more than once. > > I also can't say I'm over the moon with yet another function that does > a very tiny bit of initialisation outside of the rest of the code that > performs the vcpu init. Following things is an absolute maze... I'm fine with this being inlined into __kvm_vcpu_set_target() so long as we maintain the clear distinction between one-time setup and vCPU reset. -- Thanks, Oliver