Re: [RFC][PATCH] KVM: Introduce direct MSI message injection for in-kernel irqchips

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

On Fri, Oct 21, 2011 at 11:19:19AM +0200, Jan Kiszka wrote:
> Currently, MSI messages can only be injected to in-kernel irqchips by
> defining a corresponding IRQ route for each message. This is not only
> unhandy if the MSI messages are generated "on the fly" by user space,
> IRQ routes are a limited resource that user space as to manage
> carefully.
> 
> By providing a direct injection with, we can both avoid using up limited
> resources and simplify the necessary steps for user land. The API
> already provides a channel (flags) to revoke an injected but not yet
> delivered message which will become important for in-kernel MSI-X vector
> masking support.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

I would love to see how you envision extending this to add the masking
support at least at the API level, not necessarily the supporting code.

It would seem hard to use flags field for that since MSIX mask is per
device per vector, not per message.
Which gets us back to resource per vector which userspace has to manage
...

interrupt remapping is also per device, so it isn't any easier
with this API.

> ---
>  Documentation/virtual/kvm/api.txt |   23 +++++++++++++++++++++++
>  include/linux/kvm.h               |   15 +++++++++++++++
>  virt/kvm/kvm_main.c               |   18 ++++++++++++++++++
>  3 files changed, 56 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 7945b0b..f4c3de3 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1383,6 +1383,29 @@ The following flags are defined:
>  If datamatch flag is set, the event will be signaled only if the written value
>  to the registered address is equal to datamatch in struct kvm_ioeventfd.
>  
> +4.59 KVM_SET_MSI
> +
> +Capability: KVM_CAP_SET_MSI
> +Architectures: x86 ia64
> +Type: vm ioctl
> +Parameters: struct kvm_msi (in)
> +Returns: 0 on success, -1 on error
> +
> +Directly inject a MSI message. Only valid with in-kernel irqchip that handles
> +MSI messages.
> +
> +struct kvm_msi {
> +	__u32 address_lo;
> +	__u32 address_hi;
> +	__u32 data;
> +	__u32 flags;
> +	__u8  pad[16];
> +};
> +
> +The following flags are defined:
> +
> +#define KVM_MSI_FLAG_RAISE     (1 << 0)
> +
>  4.62 KVM_CREATE_SPAPR_TCE
>  
>  Capability: KVM_CAP_SPAPR_TCE
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 6884054..83875ed 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -557,6 +557,9 @@ struct kvm_ppc_pvinfo {
>  #define KVM_CAP_PPC_HIOR 67
>  #define KVM_CAP_PPC_PAPR 68
>  #define KVM_CAP_S390_GMAP 71
> +#ifdef __KVM_HAVE_MSI
> +#define KVM_CAP_SET_MSI 72
> +#endif
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -636,6 +639,16 @@ struct kvm_clock_data {
>  	__u32 pad[9];
>  };
>  
> +#define KVM_MSI_FLAG_RAISE     (1 << 0)
> +
> +struct kvm_msi {
> +	__u32 address_lo;
> +	__u32 address_hi;
> +	__u32 data;
> +	__u32 flags;
> +	__u8  pad[16];
> +};
> +
>  /*
>   * ioctls for VM fds
>   */
> @@ -696,6 +709,8 @@ struct kvm_clock_data {
>  /* Available with KVM_CAP_TSC_CONTROL */
>  #define KVM_SET_TSC_KHZ           _IO(KVMIO,  0xa2)
>  #define KVM_GET_TSC_KHZ           _IO(KVMIO,  0xa3)
> +/* Available with KVM_CAP_SET_MSI */
> +#define KVM_SET_MSI               _IOW(KVMIO,  0xa4, struct kvm_msi)
>  
>  /*
>   * ioctls for vcpu fds
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d9cfb78..0e3a947 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2058,6 +2058,24 @@ static long kvm_vm_ioctl(struct file *filp,
>  		mutex_unlock(&kvm->lock);
>  		break;
>  #endif
> +#ifdef __KVM_HAVE_MSI
> +	case KVM_SET_MSI: {
> +		struct kvm_kernel_irq_routing_entry route;
> +		struct kvm_msi msi;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&msi, argp, sizeof msi))
> +			goto out;
> +		route.msi.address_lo = msi.address_lo;
> +		route.msi.address_hi = msi.address_hi;
> +		route.msi.data = msi.data;
> +		r = 0;
> +		if (msi.flags & KVM_MSI_FLAG_RAISE)
> +			r =  kvm_set_msi(&route, kvm,
> +					 KVM_USERSPACE_IRQ_SOURCE_ID, 1);
> +		break;
> +	}
> +#endif
>  	default:
>  		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
>  		if (r == -ENOTTY)
> -- 
> 1.7.3.4