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Message-ID: <1345583694.29292.91.camel@ul30vt.home>
Date: Tue, 21 Aug 2012 15:14:54 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: avi@...hat.com, gleb@...hat.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd
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.
> > > > 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 <alex.williamson@...hat.com>
> > > > ---
> > > >
> > > > 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
> > > > 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();
> >
> >
--
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