Re: [PATCH v4 01/12] KVM: extend struct kvm_msi to hold a 32-bit device ID

[Christoffer Dall <christoffer.dall@linaro.org>]

On Sat, Mar 26, 2016 at 02:13:59AM +0000, Andre Przywara wrote:
> The ARM GICv3 ITS MSI controller requires a device ID to be able to
> assign the proper interrupt vector. On real hardware, this ID is
> sampled from the bus. To be able to emulate an ITS controller, extend
> the KVM MSI interface to let userspace provide such a device ID. For
> PCI devices, the device ID is simply the 16-bit bus-device-function
> triplet, which should be easily available to the userland tool.
> 
> Also there is a new KVM capability which advertises whether the
> current VM requires a device ID to be set along with the MSI data.
> This flag is still reported as not available everywhere, later we will
> enable it when ITS emulation is used.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Reviewed-by: Eric Auger <eric.auger@linaro.org>
> ---
>  Documentation/virtual/kvm/api.txt | 12 ++++++++++--
>  include/uapi/linux/kvm.h          |  5 ++++-
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index cb2ef0b..8f7351d 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2163,10 +2163,18 @@ struct kvm_msi {
>  	__u32 address_hi;
>  	__u32 data;
>  	__u32 flags;
> -	__u8  pad[16];
> +	__u32 devid;

Are we imposing any unfortunate restrictions for other architectures by
using a u32 over a u64 for the device ID?

-Christoffer

> +	__u8  pad[12];
>  };
>  
> -No flags are defined so far. The corresponding field must be 0.
> +flags: KVM_MSI_VALID_DEVID: devid contains a valid value
> +devid: If KVM_MSI_VALID_DEVID is set, contains a unique device identifier
> +       for the device that wrote the MSI message.
> +       For PCI, this is usually a BFD identifier in the lower 16 bits.
> +
> +The per-VM KVM_CAP_MSI_DEVID capability advertises the need to provide
> +the device ID. If this capability is not set, userland cannot rely on
> +the kernel to allow the KVM_MSI_VALID_DEVID flag being set.
>  
>  
>  4.71 KVM_CREATE_PIT2
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 50f44a2..6a02871 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -852,6 +852,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_S390_RI 124
>  #define KVM_CAP_ARM_PMU_V3 125
>  #define KVM_CAP_VCPU_ATTRIBUTES 126
> +#define KVM_CAP_MSI_DEVID 127
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -1010,12 +1011,14 @@ struct kvm_one_reg {
>  	__u64 addr;
>  };
>  
> +#define KVM_MSI_VALID_DEVID	(1U << 0)
>  struct kvm_msi {
>  	__u32 address_lo;
>  	__u32 address_hi;
>  	__u32 data;
>  	__u32 flags;
> -	__u8  pad[16];
> +	__u32 devid;
> +	__u8  pad[12];
>  };
>  
>  struct kvm_arm_device_addr {
> -- 
> 2.7.3
>