From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6ACA1CDB483 for ; Tue, 17 Oct 2023 05:52:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234463AbjJQFwh (ORCPT ); Tue, 17 Oct 2023 01:52:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230343AbjJQFwe (ORCPT ); Tue, 17 Oct 2023 01:52:34 -0400 Received: from out-209.mta0.migadu.com (out-209.mta0.migadu.com [IPv6:2001:41d0:1004:224b::d1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A332F9E; Mon, 16 Oct 2023 22:52:32 -0700 (PDT) Date: Tue, 17 Oct 2023 05:52:24 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1697521950; 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=fVj3QOXnTr/Xh7eUU3olV979cXmOJTmj7/jYZIF4yF4=; b=OdmnPA8A+91moypBiaGZn8ibVGmZmN0HlfkfnzmzJQJBXglPtzHGRWJlvkfP5NADESecPn LfHytZzAvYtJ/AuWS3MjDUzpoPd1KHYxGwXalx8C92EpY8eHM4WMityUHrBuqJvQO9N3Y6 ePHgtv1NQGXK0zyXqDl1SenjwijfMhQ= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Raghavendra Rao Ananta Cc: Sebastian Ott , Marc Zyngier , 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 v7 07/12] KVM: arm64: PMU: Set PMCR_EL0.N for vCPU based on the associated PMU Message-ID: References: <20231009230858.3444834-1-rananta@google.com> <20231009230858.3444834-8-rananta@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 16, 2023 at 02:35:52PM -0700, Raghavendra Rao Ananta wrote: [...] > > What's the point of doing this in the first place? The implementation of > > kvm_vcpu_read_pmcr() is populating PMCR_EL0.N using the VM-scoped value. > > > I guess originally the change replaced read_sysreg(pmcr_el0) with > kvm_vcpu_read_pmcr(vcpu) to maintain consistency with others. > But if you and Sebastian feel that it's an overkill and directly > getting the value via vcpu->kvm->arch.pmcr_n is more readable, I'm > happy to make the change. No, I'd rather you delete the line where PMCR_EL0.N altogether. reset_pmcr() tries to initialize the field, but your kvm_vcpu_read_pmcr() winds up replacing it with pmcr_n. > @@ -1105,8 +1109,16 @@ u8 kvm_arm_pmu_get_pmuver_limit(void) > /** > * kvm_vcpu_read_pmcr - Read PMCR_EL0 register for the vCPU > * @vcpu: The vcpu pointer > + * > + * The function returns the value of PMCR.N based on the per-VM tracked > + * value (kvm->arch.pmcr_n). This is to ensure that the register field > + * remains consistent for the VM, even on heterogeneous systems where > + * the value may vary when read from different CPUs (during vCPU reset). Since I'm looking at this again, I don't believe the comment is adding much. KVM doesn't read pmcr_el0 directly anymore, and kvm_arch is clearly VM-scoped context. > */ > u64 kvm_vcpu_read_pmcr(struct kvm_vcpu *vcpu) > { > - return __vcpu_sys_reg(vcpu, PMCR_EL0); > + u64 pmcr = __vcpu_sys_reg(vcpu, PMCR_EL0) & > + ~(ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT); > + > + return pmcr | ((u64)vcpu->kvm->arch.pmcr_n << ARMV8_PMU_PMCR_N_SHIFT); > } -- Thanks, Oliver