From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754044AbdA3TEy (ORCPT ); Mon, 30 Jan 2017 14:04:54 -0500 Received: from mail-lf0-f53.google.com ([209.85.215.53]:34411 "EHLO mail-lf0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753848AbdA3TEx (ORCPT ); Mon, 30 Jan 2017 14:04:53 -0500 Date: Mon, 30 Jan 2017 20:04:50 +0100 From: Christoffer Dall To: Marc Zyngier Cc: Jintack Lim , pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, andre.przywara@arm.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Peter Maydell Subject: Re: [RFC v2 05/10] KVM: arm/arm64: Initialize the emulated EL1 physical timer Message-ID: <20170130190450.GF16459@cbox> References: <1485479100-4966-1-git-send-email-jintack@cs.columbia.edu> <1485479100-4966-6-git-send-email-jintack@cs.columbia.edu> <86wpde83xn.fsf@arm.com> <20170130145816.GC16459@cbox> <57b57b31-b8ad-f5c8-a1fc-4cde9a564dd2@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57b57b31-b8ad-f5c8-a1fc-4cde9a564dd2@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 30, 2017 at 05:44:20PM +0000, Marc Zyngier wrote: > On 30/01/17 14:58, Christoffer Dall wrote: > > On Sun, Jan 29, 2017 at 12:07:48PM +0000, Marc Zyngier wrote: > >> On Fri, Jan 27 2017 at 01:04:55 AM, Jintack Lim wrote: > >>> Initialize the emulated EL1 physical timer with the default irq number. > >>> > >>> Signed-off-by: Jintack Lim > >>> --- > >>> arch/arm/kvm/reset.c | 9 ++++++++- > >>> arch/arm64/kvm/reset.c | 9 ++++++++- > >>> include/kvm/arm_arch_timer.h | 3 ++- > >>> virt/kvm/arm/arch_timer.c | 9 +++++++-- > >>> 4 files changed, 25 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/arch/arm/kvm/reset.c b/arch/arm/kvm/reset.c > >>> index 4b5e802..1da8b2d 100644 > >>> --- a/arch/arm/kvm/reset.c > >>> +++ b/arch/arm/kvm/reset.c > >>> @@ -37,6 +37,11 @@ > >>> .usr_regs.ARM_cpsr = SVC_MODE | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT, > >>> }; > >>> > >>> +static const struct kvm_irq_level cortexa_ptimer_irq = { > >>> + { .irq = 30 }, > >>> + .level = 1, > >>> +}; > >> > >> At some point, we'll have to make that discoverable/configurable. Maybe > >> the time for a discoverable arch timer has come (see below). > >> > >>> + > >>> static const struct kvm_irq_level cortexa_vtimer_irq = { > >>> { .irq = 27 }, > >>> .level = 1, > >>> @@ -58,6 +63,7 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > >>> { > >>> struct kvm_regs *reset_regs; > >>> const struct kvm_irq_level *cpu_vtimer_irq; > >>> + const struct kvm_irq_level *cpu_ptimer_irq; > >>> > >>> switch (vcpu->arch.target) { > >>> case KVM_ARM_TARGET_CORTEX_A7: > >>> @@ -65,6 +71,7 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > >>> reset_regs = &cortexa_regs_reset; > >>> vcpu->arch.midr = read_cpuid_id(); > >>> cpu_vtimer_irq = &cortexa_vtimer_irq; > >>> + cpu_ptimer_irq = &cortexa_ptimer_irq; > >>> break; > >>> default: > >>> return -ENODEV; > >>> @@ -77,5 +84,5 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > >>> kvm_reset_coprocs(vcpu); > >>> > >>> /* Reset arch_timer context */ > >>> - return kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq); > >>> + return kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq, cpu_ptimer_irq); > >>> } > >>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c > >>> index e95d4f6..d9e9697 100644 > >>> --- a/arch/arm64/kvm/reset.c > >>> +++ b/arch/arm64/kvm/reset.c > >>> @@ -46,6 +46,11 @@ > >>> COMPAT_PSR_I_BIT | COMPAT_PSR_F_BIT), > >>> }; > >>> > >>> +static const struct kvm_irq_level default_ptimer_irq = { > >>> + .irq = 30, > >>> + .level = 1, > >>> +}; > >>> + > >>> static const struct kvm_irq_level default_vtimer_irq = { > >>> .irq = 27, > >>> .level = 1, > >>> @@ -104,6 +109,7 @@ int kvm_arch_dev_ioctl_check_extension(struct kvm *kvm, long ext) > >>> int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > >>> { > >>> const struct kvm_irq_level *cpu_vtimer_irq; > >>> + const struct kvm_irq_level *cpu_ptimer_irq; > >>> const struct kvm_regs *cpu_reset; > >>> > >>> switch (vcpu->arch.target) { > >>> @@ -117,6 +123,7 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > >>> } > >>> > >>> cpu_vtimer_irq = &default_vtimer_irq; > >>> + cpu_ptimer_irq = &default_ptimer_irq; > >>> break; > >>> } > >>> > >>> @@ -130,5 +137,5 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > >>> kvm_pmu_vcpu_reset(vcpu); > >>> > >>> /* Reset timer */ > >>> - return kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq); > >>> + return kvm_timer_vcpu_reset(vcpu, cpu_vtimer_irq, cpu_ptimer_irq); > >>> } > >>> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h > >>> index 69f648b..a364593 100644 > >>> --- a/include/kvm/arm_arch_timer.h > >>> +++ b/include/kvm/arm_arch_timer.h > >>> @@ -59,7 +59,8 @@ struct arch_timer_cpu { > >>> int kvm_timer_enable(struct kvm_vcpu *vcpu); > >>> void kvm_timer_init(struct kvm *kvm); > >>> int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, > >>> - const struct kvm_irq_level *irq); > >>> + const struct kvm_irq_level *virt_irq, > >>> + const struct kvm_irq_level *phys_irq); > >>> void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu); > >>> void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu); > >>> void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu); > >>> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > >>> index f72005a..0f6e935 100644 > >>> --- a/virt/kvm/arm/arch_timer.c > >>> +++ b/virt/kvm/arm/arch_timer.c > >>> @@ -329,9 +329,11 @@ void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu) > >>> } > >>> > >>> int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, > >>> - const struct kvm_irq_level *irq) > >>> + const struct kvm_irq_level *virt_irq, > >>> + const struct kvm_irq_level *phys_irq) > >>> { > >>> struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); > >>> + struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); > >>> > >>> /* > >>> * The vcpu timer irq number cannot be determined in > >>> @@ -339,7 +341,8 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, > >>> * kvm_vcpu_set_target(). To handle this, we determine > >>> * vcpu timer irq number when the vcpu is reset. > >>> */ > >>> - vtimer->irq.irq = irq->irq; > >>> + vtimer->irq.irq = virt_irq->irq; > >>> + ptimer->irq.irq = phys_irq->irq; > >>> > >>> /* > >>> * The bits in CNTV_CTL are architecturally reset to UNKNOWN for ARMv8 > >>> @@ -348,6 +351,7 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, > >>> * the ARMv7 architecture. > >>> */ > >>> vtimer->cnt_ctl = 0; > >>> + ptimer->cnt_ctl = 0; > >>> kvm_timer_update_state(vcpu); > >>> > >>> return 0; > >>> @@ -369,6 +373,7 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu) > >>> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; > >>> > >>> update_vtimer_cntvoff(vcpu, kvm_phys_timer_read()); > >>> + vcpu_ptimer(vcpu)->cntvoff = 0; > >> > >> This is quite contentious, IMHO. Do we really want to expose the delta > >> between the virtual and physical counters? That's a clear indication to > >> the guest that it is virtualized. I"m not sure it matters, but I think > >> we should at least make a conscious choice, and maybe give the > >> opportunity to userspace to select the desired behaviour. > >> > > > > So my understanding of the architecture is that you should always have > > two timer/counter pairs available at EL1. They may be synchronized, and > > they may not. If you want an accurate reading of wall clock time, look > > at the physical counter, and that can generally be expected to be fast, > > precise, and syncrhonized (on working hardware, of course). > > > > Now, there can be a constant or potentially monotonically increasing > > offset between the physial and virtual counters, which may mean you're > > running under a hypervisor or (in the first case) that firmware > > programmed or neglected to program cntvoff. I don't think it's an > > inherent problem to expose that difference to a guest, and I think it's > > more important that reading the physical counter is fast and doesn't > > trap. > > > > The question is which contract we can have with a guest OS, and which > > legacy we have to keep supporting (Linux, UEFI, ?). > > > > Probably Linux should keep relying on the virtual counter/timer only, > > unless something is advertised in DT/ACPI, about it being able to use > > the physical timer/counter pair, even when booted at EL1. We could > > explore the opportunities to build on that to let the guest figure > > out stolen time by reading the two counters and by programming the > > proper timer depending on the desired semantics (i.e. virtual or > > physical time). > > > > In terms of this patch, I actually think it's fine, but we may need to > > build something more on top later. It is possible, though, that I'm > > entirely missing the point about Linux timekeeping infrastructure and > > that my reading of the architecture is bogus. > > > > What do you think? > > I don't disagree with any of this (hopefully I was clearer in my reply > to the cover letter). Yeah, my long-winded reply was sort of to convince myself about my own understanding :) > Wventually, we'll have to support an offset-able > physical counter to support nested virtualization, but this can come at > a later time. > Why do we need the offset-able physical counter for nested virtualization? I would think for nested virt we just need to support respecting how the guest hypervisor programs CNTVOFF? Thanks, -Christoffer