From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752277Ab2HVAkj (ORCPT ); Tue, 21 Aug 2012 20:40:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56115 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751365Ab2HVAkf (ORCPT ); Tue, 21 Aug 2012 20:40:35 -0400 Date: Wed, 22 Aug 2012 03:41:38 +0300 From: "Michael S. Tsirkin" To: Alex Williamson Cc: avi@redhat.com, gleb@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd Message-ID: <20120822004138.GM9027@redhat.com> References: <20120821190800.24958.74812.stgit@bling.home> <20120821192903.24958.90138.stgit@bling.home> <20120821195813.GD9027@redhat.com> <1345579579.29292.67.camel@ul30vt.home> <20120821204125.GF9027@redhat.com> <1345583694.29292.91.camel@ul30vt.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1345583694.29292.91.camel@ul30vt.home> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 21, 2012 at 03:14:54PM -0600, Alex Williamson wrote: > On Tue, 2012-08-21 at 23:41 +0300, Michael S. Tsirkin wrote: > > On Tue, Aug 21, 2012 at 02:06:19PM -0600, Alex Williamson wrote: > > > On Tue, 2012-08-21 at 22:58 +0300, Michael S. Tsirkin wrote: > > > > On Tue, Aug 21, 2012 at 01:29:06PM -0600, Alex Williamson wrote: > > > > > KVM_IRQFD currently uses the reserved KVM_USERSPACE_IRQ_SOURCE_ID > > > > > which is also shared with userspace injection methods like > > > > > KVM_IRQ_LINE. This can cause a conflict if an irqfd triggers on > > > > > a GSI asserted through KVM_IRQ_LINE. > > > > > > > > What kind of conflict do you envision? Pls note level interrupts are > > > > unsupported ATM. > > > > > > If KVM_IRQ_LINE asserts a level interrupt and KVM_IRQFD triggers on the > > > same GSI then the pin is no longer asserted as userspace thinks it is. > > > Do we just chalk this up to userspace error? > > > > Yes: using a level GSI with current irqfd is a userspace error > > because you can lose interrupts anyway. > > > > Are edge GSIs affected? > > I wouldn't think so. No? If userspace does . set line to 1 . trigger irqfd . set line to 1 . trigger irqfd . set line to 1 . trigger irqfd . set line to 1 it gets 4 interrupts now With your patch it will get 1, right? > > > > > Move irqfd to it's own reserved IRQ source ID. Add a capability for > > > > > userspace to test for this fix. > > > > > > > > > > Signed-off-by: Alex Williamson > > > > > --- > > > > > > > > > > arch/x86/kvm/x86.c | 3 +++ > > > > > include/linux/kvm.h | 1 + > > > > > include/linux/kvm_host.h | 1 + > > > > > virt/kvm/eventfd.c | 6 +++--- > > > > > 4 files changed, 8 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > > > index 42bce48..cd98673 100644 > > > > > --- a/arch/x86/kvm/x86.c > > > > > +++ b/arch/x86/kvm/x86.c > > > > > @@ -2174,6 +2174,7 @@ int kvm_dev_ioctl_check_extension(long ext) > > > > > case KVM_CAP_GET_TSC_KHZ: > > > > > case KVM_CAP_PCI_2_3: > > > > > case KVM_CAP_KVMCLOCK_CTRL: > > > > > + case KVM_CAP_IRQFD_IRQ_SOURCE_ID: > > > > > r = 1; > > > > > break; > > > > > case KVM_CAP_COALESCED_MMIO: > > > > > @@ -6258,6 +6259,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > > > > > > > > > > /* Reserve bit 0 of irq_sources_bitmap for userspace irq source */ > > > > > set_bit(KVM_USERSPACE_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap); > > > > > + /* Reserve bit 1 of irq_sources_bitmap for irqfd irq source */ > > > > > + set_bit(KVM_IRQFD_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap); > > > > > > > > > > raw_spin_lock_init(&kvm->arch.tsc_write_lock); > > > > > > > > > > diff --git a/include/linux/kvm.h b/include/linux/kvm.h > > > > > index 2ce09aa..ae66b9c 100644 > > > > > --- a/include/linux/kvm.h > > > > > +++ b/include/linux/kvm.h > > > > > @@ -618,6 +618,7 @@ struct kvm_ppc_smmu_info { > > > > > #define KVM_CAP_PPC_GET_SMMU_INFO 78 > > > > > #define KVM_CAP_S390_COW 79 > > > > > #define KVM_CAP_PPC_ALLOC_HTAB 80 > > > > > +#define KVM_CAP_IRQFD_IRQ_SOURCE_ID 81 > > > > > > > > > > #ifdef KVM_CAP_IRQ_ROUTING > > > > > > > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > > > > index b70b48b..b763230 100644 > > > > > --- a/include/linux/kvm_host.h > > > > > +++ b/include/linux/kvm_host.h > > > > > @@ -71,6 +71,7 @@ > > > > > #define KVM_REQ_PMI 17 > > > > > > > > > > #define KVM_USERSPACE_IRQ_SOURCE_ID 0 > > > > > +#define KVM_IRQFD_IRQ_SOURCE_ID 1 > > > > > > > > > > struct kvm; > > > > > struct kvm_vcpu; > > > > > > > > Above looks fine but I'm not sure why is the below needed. > > > > This changes irqfd behaviour for edge GSIs slightly > > > > in a userspace-visible way. Maybe make it a separate patch > > > > so it can be considered on merits? > > > > > > Hmm, the above does nothing without the below. > > > > Yes. But you can use the above with the new irqfds you are adding. > > Nope, racy. > > > > I thought I was just > > > implementing your idea that IRQFDs should all share a single IRQ source > > > ID... > > > > Sorry I only meant for level irqfds. You are changing edge here. > > Ok, I misunderstood then. > > > > why is that no longer a good idea? Thanks, > > > > > > Alex > > > > Maybe it is a good idea. I am just asking for the motivation. > > I assumed you were pointing out the level vs edge interaction. If we > call that a userspace bug, I can just drop this. Thanks, > > Alex level is userspace bug I think :) > > > > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > > > > > index 7d7e2aa..2245cfa 100644 > > > > > --- a/virt/kvm/eventfd.c > > > > > +++ b/virt/kvm/eventfd.c > > > > > @@ -67,8 +67,8 @@ irqfd_inject(struct work_struct *work) > > > > > struct _irqfd *irqfd = container_of(work, struct _irqfd, inject); > > > > > struct kvm *kvm = irqfd->kvm; > > > > > > > > > > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1); > > > > > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0); > > > > > + kvm_set_irq(kvm, KVM_IRQFD_IRQ_SOURCE_ID, irqfd->gsi, 1); > > > > > + kvm_set_irq(kvm, KVM_IRQFD_IRQ_SOURCE_ID, irqfd->gsi, 0); > > > > > } > > > > > > > > > > /* > > > > > @@ -138,7 +138,7 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key) > > > > > irq = rcu_dereference(irqfd->irq_entry); > > > > > /* An event has been signaled, inject an interrupt */ > > > > > if (irq) > > > > > - kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1); > > > > > + kvm_set_msi(irq, kvm, KVM_IRQFD_IRQ_SOURCE_ID, 1); > > > > > else > > > > > schedule_work(&irqfd->inject); > > > > > rcu_read_unlock(); > > > > > > > >