Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd

Michael S. Tsirkin
2012-08-21T19:57:12Z

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.

> 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@redhat.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?

> 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();