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

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

Hi Christoffer,

On 03/04/16 10:15, Christoffer Dall wrote:
> 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?

Mmmh, good point. I guess not only for other architectures, but also for
the future in general.

Are there any objections against increasing this to a u64?

Cheers,
Andre.

>> +	__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
>>
>