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 35EC0C41513 for ; Tue, 17 Oct 2023 17:09:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343864AbjJQRJW (ORCPT ); Tue, 17 Oct 2023 13:09:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39776 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234942AbjJQRJU (ORCPT ); Tue, 17 Oct 2023 13:09:20 -0400 Received: from out-208.mta0.migadu.com (out-208.mta0.migadu.com [IPv6:2001:41d0:1004:224b::d0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 66F70FD for ; Tue, 17 Oct 2023 10:09:17 -0700 (PDT) Date: Tue, 17 Oct 2023 17:09:09 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1697562555; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7Rfv7r/GuU3poBoBBegpc3MH7nKblNdFhx9LayDfN/g=; b=TFgn2b52np5IlEuu1uUS0tBRQpxK65WkA4Rmi+nvkk/K2SazzQgS5KeQwEiHqQ4qLjybb1 Dr7lvKVLwFmwGHOmJ4Gks+3K03eT7PtCqdqC4B+auUvybaYnVf/F8Ngan61k6vSXRyYqP/ 9jzXApHjjRRK96UwkrZJfelaWWrcczk= 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 17, 2023 at 09:58:08AM -0700, Raghavendra Rao Ananta wrote: > On Mon, Oct 16, 2023 at 10:52 PM Oliver Upton wrote: > > > > 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. > > > I didn't get this comment. We still do initialize pmcr, but using the > pmcr.n read via kvm_vcpu_read_pmcr() instead of the actual system > register. You have two bits of code trying to do the exact same thing: 1) reset_pmcr() initializes __vcpu_sys_reg(vcpu, PMCR_EL0) with the N field set up. 2) kvm_vcpu_read_pmcr() takes whatever is in __vcpu_sys_reg(vcpu, PMCR_EL0), *masks out* the N field and re-initializes it with vcpu->kvm->arch.pmcr_n Why do you need (1) if you do (2)? -- Thanks, Oliver