Re: [PATCH 1/3] KVM: Emulation MSI-X mask bits for assigned devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 28, 2010 at 05:44:10PM +0800, Sheng Yang wrote:
> This patch enable per-vector mask for assigned devices using MSI-X.
> 
> Signed-off-by: Sheng Yang <sheng@linux.intel.com>

I think I see an issue here, noted below.  Some general comments:
- The mask bit seems broken for injecting interrupts from
  userspace (with interrupts/ioctls).
  I think we must test it on injection path.
- We'll need a way to support the pending bit.
  Disabling interrupts will not let us do it.

> ---
>  arch/x86/kvm/x86.c       |    1 +
>  include/linux/kvm.h      |    9 ++++++++-
>  include/linux/kvm_host.h |    1 +
>  virt/kvm/assigned-dev.c  |   39 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 49 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8412c91..e6933e6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1927,6 +1927,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_DEBUGREGS:
>  	case KVM_CAP_X86_ROBUST_SINGLESTEP:
>  	case KVM_CAP_XSAVE:
> +	case KVM_CAP_DEVICE_MSIX_MASK:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 919ae53..f2b7cdc 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -540,6 +540,9 @@ struct kvm_ppc_pvinfo {
>  #endif
>  #define KVM_CAP_PPC_GET_PVINFO 57
>  #define KVM_CAP_PPC_IRQ_LEVEL 58
> +#ifdef __KVM_HAVE_MSIX
> +#define KVM_CAP_DEVICE_MSIX_MASK 59
> +#endif
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -787,11 +790,15 @@ struct kvm_assigned_msix_nr {
>  };
>  
>  #define KVM_MAX_MSIX_PER_DEV		256
> +
> +#define KVM_MSIX_FLAG_MASK	1
> +
>  struct kvm_assigned_msix_entry {
>  	__u32 assigned_dev_id;
>  	__u32 gsi;
>  	__u16 entry; /* The index of entry in the MSI-X table */
> -	__u16 padding[3];
> +	__u16 flags;
> +	__u16 padding[2];
>  };
>  
>  #endif /* __LINUX_KVM_H */
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 0b89d00..a43405c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -415,6 +415,7 @@ struct kvm_irq_ack_notifier {
>  };
>  
>  #define KVM_ASSIGNED_MSIX_PENDING		0x1
> +#define KVM_ASSIGNED_MSIX_MASK			0x2
>  struct kvm_guest_msix_entry {
>  	u32 vector;
>  	u16 entry;
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index 7c98928..15b8c32 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -17,6 +17,8 @@
>  #include <linux/pci.h>
>  #include <linux/interrupt.h>
>  #include <linux/slab.h>
> +#include <linux/irqnr.h>
> +
>  #include "irq.h"
>  
>  static struct kvm_assigned_dev_kernel *kvm_find_assigned_dev(struct list_head *head,
> @@ -666,6 +668,30 @@ msix_nr_out:
>  	return r;
>  }
>  
> +static void update_msix_mask(struct kvm_assigned_dev_kernel *assigned_dev,
> +			     int index)
> +{
> +	int irq;
> +
> +	if (!assigned_dev->dev->msix_enabled ||
> +	    !(assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX))
> +		return;
> +
> +	irq = assigned_dev->host_msix_entries[index].vector;
> +
> +	ASSERT(irq != 0);
> +
> +	if (assigned_dev->guest_msix_entries[index].flags &
> +			KVM_ASSIGNED_MSIX_MASK)
> +		disable_irq(irq);
> +	else {
> +		enable_irq(irq);
> +		if (assigned_dev->guest_msix_entries[index].flags &
> +				KVM_ASSIGNED_MSIX_PENDING)
> +			schedule_work(&assigned_dev->interrupt_work);
> +	}
> +}
> +

What happens if guest masks an entry and then we hot-unplug the
device and remove it from guest? It looks like interrupt
will stay disabled?


>  static int kvm_vm_ioctl_set_msix_entry(struct kvm *kvm,
>  				       struct kvm_assigned_msix_entry *entry)
>  {
> @@ -688,6 +714,19 @@ static int kvm_vm_ioctl_set_msix_entry(struct kvm *kvm,
>  			adev->guest_msix_entries[i].entry = entry->entry;
>  			adev->guest_msix_entries[i].vector = entry->gsi;
>  			adev->host_msix_entries[i].entry = entry->entry;
> +			if ((entry->flags & KVM_MSIX_FLAG_MASK) &&
> +					!(adev->guest_msix_entries[i].flags &
> +					KVM_ASSIGNED_MSIX_MASK)) {
> +				adev->guest_msix_entries[i].flags |=
> +					KVM_ASSIGNED_MSIX_MASK;
> +				update_msix_mask(adev, i);
> +			} else if (!(entry->flags & KVM_MSIX_FLAG_MASK) &&
> +					(adev->guest_msix_entries[i].flags &
> +					KVM_ASSIGNED_MSIX_MASK)) {
> +				adev->guest_msix_entries[i].flags &=
> +					~KVM_ASSIGNED_MSIX_MASK;
> +				update_msix_mask(adev, i);
> +			}
>  			break;
>  		}
>  	if (i == adev->entries_nr) {
> -- 
> 1.7.0.1
> 
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