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[209.132.180.67]) by mx.google.com with ESMTP id q16si15486231pfg.221.2018.03.08.01.52.05; Thu, 08 Mar 2018 01:52:19 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965963AbeCHJtx (ORCPT + 99 others); Thu, 8 Mar 2018 04:49:53 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:34936 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965800AbeCHJtr (ORCPT ); Thu, 8 Mar 2018 04:49:47 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 58A491529; Thu, 8 Mar 2018 01:49:47 -0800 (PST) Received: from [10.1.207.62] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 965353F25C; Thu, 8 Mar 2018 01:49:45 -0800 (PST) Subject: Re: [RFC PATCH] KVM: arm/arm64: vgic: change condition for level interrupt resampling To: Shunyong Yang Cc: ard.biesheuvel@linaro.org, will.deacon@arm.com, eric.auger@redhat.com, david.daney@cavium.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Joey Zheng , Christoffer Dall References: <1520492490-7943-1-git-send-email-shunyong.yang@hxt-semitech.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: <9ad47673-068e-f732-d2ca-9c76a8fbdfbc@arm.com> Date: Thu, 8 Mar 2018 09:49:43 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <1520492490-7943-1-git-send-email-shunyong.yang@hxt-semitech.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [updated Christoffer's email address] Hi Shunyong, On 08/03/18 07:01, Shunyong Yang wrote: > When resampling irqfds is enabled, level interrupt should be > de-asserted when resampling happens. On page 4-47 of GIC v3 > specification IHI0069D, it said, > "When the PE acknowledges an SGI, a PPI, or an SPI at the CPU > interface, the IRI changes the status of the interrupt to active > and pending if: > • It is an edge-triggered interrupt, and another edge has been > detected since the interrupt was acknowledged. > • It is a level-sensitive interrupt, and the level has not been > deasserted since the interrupt was acknowledged." > > GIC v2 specification IHI0048B.b has similar description on page > 3-42 for state machine transition. > > When some VFIO device, like mtty(8250 VFIO mdev emulation driver > in samples/vfio-mdev) triggers a level interrupt, the status > transition in LR is pending-->active-->active and pending. > Then it will wait resampling to de-assert the interrupt. > > Current design of lr_signals_eoi_mi() will return false if state > in LR is not invalid(Inactive). It causes resampling will not happen > in mtty case. Let me rephrase this, and tell me if I understood it correctly: - A level interrupt is injected, activated by the guest (LR state=active) - guest exits, re-enters, (LR state=pending+active) - guest EOIs the interrupt (LR state=pending) - maintenance interrupt - we don't signal the resampling because we're not in an invalid state Is that correct? That's an interesting case, because it seems to invalidate some of the optimization that went in over a year ago. 096f31c4360f KVM: arm/arm64: vgic: Get rid of MISR and EISR fields b6095b084d87 KVM: arm/arm64: vgic: Get rid of unnecessary save_maint_int_state af0614991ab6 KVM: arm/arm64: vgic: Get rid of unnecessary process_maintenance operation We could compare the value of the LR before the guest entry with the value at exit time, but we still could miss it if we have a transition such as P+A -> P -> A and assume a long enough propagation delay for the maintenance interrupt (which is very likely). In essence, we have lost the benefit of EISR, which was to give us a way to deal with asynchronous signalling. > > This will cause interrupt fired continuously to guest even 8250 IIR > has no interrupt. When 8250's interrupt is configured in shared mode, > it will pass interrupt to other drivers to handle. However, there > is no other driver involved. Then, a "nobody cared" kernel complaint > occurs. > > / # cat /dev/ttyS0 > [ 4.826836] random: crng init done > [ 6.373620] irq 41: nobody cared (try booting with the "irqpoll" > option) > [ 6.376414] CPU: 0 PID: 1307 Comm: cat Not tainted 4.16.0-rc4 #4 > [ 6.378927] Hardware name: linux,dummy-virt (DT) > [ 6.380876] Call trace: > [ 6.381937] dump_backtrace+0x0/0x180 > [ 6.383495] show_stack+0x14/0x1c > [ 6.384902] dump_stack+0x90/0xb4 > [ 6.386312] __report_bad_irq+0x38/0xe0 > [ 6.387944] note_interrupt+0x1f4/0x2b8 > [ 6.389568] handle_irq_event_percpu+0x54/0x7c > [ 6.391433] handle_irq_event+0x44/0x74 > [ 6.393056] handle_fasteoi_irq+0x9c/0x154 > [ 6.394784] generic_handle_irq+0x24/0x38 > [ 6.396483] __handle_domain_irq+0x60/0xb4 > [ 6.398207] gic_handle_irq+0x98/0x1b0 > [ 6.399796] el1_irq+0xb0/0x128 > [ 6.401138] _raw_spin_unlock_irqrestore+0x18/0x40 > [ 6.403149] __setup_irq+0x41c/0x678 > [ 6.404669] request_threaded_irq+0xe0/0x190 > [ 6.406474] univ8250_setup_irq+0x208/0x234 > [ 6.408250] serial8250_do_startup+0x1b4/0x754 > [ 6.410123] serial8250_startup+0x20/0x28 > [ 6.411826] uart_startup.part.21+0x78/0x144 > [ 6.413633] uart_port_activate+0x50/0x68 > [ 6.415328] tty_port_open+0x84/0xd4 > [ 6.416851] uart_open+0x34/0x44 > [ 6.418229] tty_open+0xec/0x3c8 > [ 6.419610] chrdev_open+0xb0/0x198 > [ 6.421093] do_dentry_open+0x200/0x310 > [ 6.422714] vfs_open+0x54/0x84 > [ 6.424054] path_openat+0x2dc/0xf04 > [ 6.425569] do_filp_open+0x68/0xd8 > [ 6.427044] do_sys_open+0x16c/0x224 > [ 6.428563] SyS_openat+0x10/0x18 > [ 6.429972] el0_svc_naked+0x30/0x34 > [ 6.431494] handlers: > [ 6.432479] [<000000000e9fb4bb>] serial8250_interrupt > [ 6.434597] Disabling IRQ #41 > > This patch changes the lr state condition in lr_signals_eoi_mi() from > invalid(Inactive) to active and pending to avoid this. > > I am not sure about the original design of the condition of > invalid(active). So, This RFC is sent out for comments. > > Cc: Joey Zheng > Signed-off-by: Shunyong Yang > --- > virt/kvm/arm/vgic/vgic-v2.c | 4 ++-- > virt/kvm/arm/vgic/vgic-v3.c | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c > index e9d840a75e7b..740ee9a5f551 100644 > --- a/virt/kvm/arm/vgic/vgic-v2.c > +++ b/virt/kvm/arm/vgic/vgic-v2.c > @@ -46,8 +46,8 @@ void vgic_v2_set_underflow(struct kvm_vcpu *vcpu) > > static bool lr_signals_eoi_mi(u32 lr_val) > { > - return !(lr_val & GICH_LR_STATE) && (lr_val & GICH_LR_EOI) && > - !(lr_val & GICH_LR_HW); > + return !((lr_val & GICH_LR_STATE) ^ GICH_LR_STATE) && That feels very wrong. You're now signalling the resampling in both invalid and pending+active, and the latter state doesn't mean you've EOIed anything. You're now over-signalling, and signalling the wrong event. > + (lr_val & GICH_LR_EOI) && !(lr_val & GICH_LR_HW); > } > > /* > diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c > index 6b329414e57a..43111bba7af9 100644 > --- a/virt/kvm/arm/vgic/vgic-v3.c > +++ b/virt/kvm/arm/vgic/vgic-v3.c > @@ -35,8 +35,8 @@ void vgic_v3_set_underflow(struct kvm_vcpu *vcpu) > > static bool lr_signals_eoi_mi(u64 lr_val) > { > - return !(lr_val & ICH_LR_STATE) && (lr_val & ICH_LR_EOI) && > - !(lr_val & ICH_LR_HW); > + return !((lr_val & ICH_LR_STATE) ^ ICH_LR_STATE) && > + (lr_val & ICH_LR_EOI) && !(lr_val & ICH_LR_HW); > } > > void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu) > Assuming I understand the issue correctly, I cannot really see how to solve this without reintroducing EISR, which sucks majorly. I'll try to cook something shortly and we can all have a good fight about how crap this is. Thanks, M. -- Jazz is not dead. It just smells funny...