Re: [RFC 1/6] KVM: api: add kvm_irq_routing_extended_msi

[Andre Przywara <andre.przywara@arm.com>]

Hi Eric,

On 18/06/15 18:40, Eric Auger wrote:
> On ARM, the MSI msg (address and data) comes along with
> out-of-band device ID information. The device ID encodes the device
> that composes the MSI msg. Let's create a new routing entry structure
> that enables to encode that information on top of standard MSI
> message
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> ---
>  Documentation/virtual/kvm/api.txt | 9 +++++++++
>  include/uapi/linux/kvm.h          | 9 +++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index d20fd94..bcec91e 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1419,6 +1419,7 @@ struct kvm_irq_routing_entry {
>  		struct kvm_irq_routing_irqchip irqchip;
>  		struct kvm_irq_routing_msi msi;
>  		struct kvm_irq_routing_s390_adapter adapter;
> +		struct kvm_irq_routing_extended_msi ext_msi;
>  		__u32 pad[8];
>  	} u;
>  };
> @@ -1427,6 +1428,7 @@ struct kvm_irq_routing_entry {
>  #define KVM_IRQ_ROUTING_IRQCHIP 1
>  #define KVM_IRQ_ROUTING_MSI 2
>  #define KVM_IRQ_ROUTING_S390_ADAPTER 3
> +#define KVM_IRQ_ROUTING_EXTENDED_MSI 4
>  
>  No flags are specified so far, the corresponding field must be set to zero.
>  
> @@ -1442,6 +1444,13 @@ struct kvm_irq_routing_msi {
>  	__u32 pad;
>  };
>  
> +struct kvm_irq_routing_extended_msi {
> +	__u32 address_lo;
> +	__u32 address_hi;
> +	__u32 data;
> +	__u32 devid;
> +};
> +

I wonder if we could re-use the existing struct kvm_irq_routing_msi,
which has an u32 pad field already. Since we use a different type
number, this should not break. Admittedly not the nicest thing, but
reduces interface bloat:

struct kvm_irq_routing_msi {
	__u32 address_lo;
	__u32 address_hi;
	__u32 data;
	union {
		__u32 pad;
		__u32 devid;
	};
};

to maintain backward compatibility on the userland source level.

Cheers,
Andre.

>  struct kvm_irq_routing_s390_adapter {
>  	__u64 ind_addr;
>  	__u64 summary_addr;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 2a23705..e3f65a0 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -829,6 +829,13 @@ struct kvm_irq_routing_msi {
>  	__u32 pad;
>  };
>  
> +struct kvm_irq_routing_extended_msi {
> +	__u32 address_lo;
> +	__u32 address_hi;
> +	__u32 data;
> +	__u32 devid;
> +};
> +
>  struct kvm_irq_routing_s390_adapter {
>  	__u64 ind_addr;
>  	__u64 summary_addr;
> @@ -841,6 +848,7 @@ struct kvm_irq_routing_s390_adapter {
>  #define KVM_IRQ_ROUTING_IRQCHIP 1
>  #define KVM_IRQ_ROUTING_MSI 2
>  #define KVM_IRQ_ROUTING_S390_ADAPTER 3
> +#define KVM_IRQ_ROUTING_EXTENDED_MSI 4
>  
>  struct kvm_irq_routing_entry {
>  	__u32 gsi;
> @@ -851,6 +859,7 @@ struct kvm_irq_routing_entry {
>  		struct kvm_irq_routing_irqchip irqchip;
>  		struct kvm_irq_routing_msi msi;
>  		struct kvm_irq_routing_s390_adapter adapter;
> +		struct kvm_irq_routing_extended_msi ext_msi;
>  		__u32 pad[8];
>  	} u;
>  };
> 
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