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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3BAECC433FE for ; Fri, 19 Nov 2021 12:17:10 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id A0A7261AA3 for ; Fri, 19 Nov 2021 12:17:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org A0A7261AA3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 22C1C4B16C; Fri, 19 Nov 2021 07:17:09 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id sSjrkU3OB1lX; Fri, 19 Nov 2021 07:17:07 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 903724B0EF; Fri, 19 Nov 2021 07:17:07 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 889464B0EF for ; Fri, 19 Nov 2021 07:17:06 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id v9PC1QjnsF6j for ; Fri, 19 Nov 2021 07:17:05 -0500 (EST) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 5312B4B0ED for ; Fri, 19 Nov 2021 07:17:05 -0500 (EST) Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8BA7F61A7D; Fri, 19 Nov 2021 12:17:03 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mo2pB-006XWO-CB; Fri, 19 Nov 2021 12:17:01 +0000 Date: Fri, 19 Nov 2021 12:17:00 +0000 Message-ID: <87fsrs732b.wl-maz@kernel.org> From: Marc Zyngier To: Nicolas Saenz Julienne Subject: Re: [RFC PATCH 2/2] KVM: arm64: export cntvoff in debugfs In-Reply-To: <20211119102117.22304-3-nsaenzju@redhat.com> References: <20211119102117.22304-1-nsaenzju@redhat.com> <20211119102117.22304-3-nsaenzju@redhat.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/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: nsaenzju@redhat.com, linux-arm-kernel@lists.infradead.org, rostedt@goodmis.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu, mingo@redhat.com, mtosatti@redhat.com, nilal@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: will@kernel.org, catalin.marinas@arm.com, mtosatti@redhat.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, mingo@redhat.com, nilal@redhat.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, 19 Nov 2021 10:21:18 +0000, Nicolas Saenz Julienne wrote: > > While using cntvct as the raw clock for tracing, it's possible to > synchronize host/guest traces just by knowing the virtual offset applied > to the guest's virtual counter. > > This is also the case on x86 when TSC is available. The offset is > exposed in debugfs as 'tsc-offset' on a per vcpu basis. So let's > implement the same for arm64. How does this work with NV, where the guest hypervisor is in control of the virtual offset? How does userspace knows which vcpu to pick so that it gets the right offset? I also wonder why we need this when userspace already has direct access to that information without any extra kernel support (read the CNTVCT view of the vcpu using the ONEREG API, subtract it from the host view of the counter, job done). > > Signed-off-by: Nicolas Saenz Julienne > --- > arch/arm64/include/asm/kvm_host.h | 1 + > arch/arm64/kvm/Makefile | 2 +- > arch/arm64/kvm/arch_timer.c | 2 +- > arch/arm64/kvm/debugfs.c | 25 +++++++++++++++++++++++++ > include/kvm/arm_arch_timer.h | 3 +++ > 5 files changed, 31 insertions(+), 2 deletions(-) > create mode 100644 arch/arm64/kvm/debugfs.c > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 2a5f7f38006f..130534c9079e 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -29,6 +29,7 @@ > #include > > #define __KVM_HAVE_ARCH_INTC_INITIALIZED > +#define __KVM_HAVE_ARCH_VCPU_DEBUGFS > > #define KVM_HALT_POLL_NS_DEFAULT 500000 > > diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile > index 989bb5dad2c8..17be7cf770f2 100644 > --- a/arch/arm64/kvm/Makefile > +++ b/arch/arm64/kvm/Makefile > @@ -14,7 +14,7 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \ > $(KVM)/vfio.o $(KVM)/irqchip.o $(KVM)/binary_stats.o \ > arm.o mmu.o mmio.o psci.o perf.o hypercalls.o pvtime.o \ > inject_fault.o va_layout.o handle_exit.o \ > - guest.o debug.o reset.o sys_regs.o \ > + guest.o debug.o debugfs.o reset.o sys_regs.o \ > vgic-sys-reg-v3.o fpsimd.o pmu.o \ > arch_timer.o trng.o\ > vgic/vgic.o vgic/vgic-init.o \ > diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c > index 3df67c127489..ee69387f7fb6 100644 > --- a/arch/arm64/kvm/arch_timer.c > +++ b/arch/arm64/kvm/arch_timer.c > @@ -82,7 +82,7 @@ u64 timer_get_cval(struct arch_timer_context *ctxt) > } > } > > -static u64 timer_get_offset(struct arch_timer_context *ctxt) > +u64 timer_get_offset(struct arch_timer_context *ctxt) > { > struct kvm_vcpu *vcpu = ctxt->vcpu; > > diff --git a/arch/arm64/kvm/debugfs.c b/arch/arm64/kvm/debugfs.c > new file mode 100644 > index 000000000000..f0f5083ea8d4 > --- /dev/null > +++ b/arch/arm64/kvm/debugfs.c > @@ -0,0 +1,25 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Copyright (C) 2021 Red Hat Inc. > + */ > + > +#include > +#include > + > +#include > + > +static int vcpu_get_cntv_offset(void *data, u64 *val) > +{ > + struct kvm_vcpu *vcpu = (struct kvm_vcpu *)data; > + > + *val = timer_get_offset(vcpu_vtimer(vcpu)); > + > + return 0; > +} > + > +DEFINE_SIMPLE_ATTRIBUTE(vcpu_cntvoff_fops, vcpu_get_cntv_offset, NULL, "%lld\n"); > + > +void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry) > +{ > + debugfs_create_file("cntvoff", 0444, debugfs_dentry, vcpu, &vcpu_cntvoff_fops); > +} This should be left in arch_timer.c until we actually need it for multiple subsystems. When (and if) that happens, we will expose per-subsystem debugfs initialisers instead of exposing the guts of the timer code. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm