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

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Date:	Tue, 21 Aug 2012 22:58:13 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Alex Williamson <alex.williamson@...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, 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@...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?

> 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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