Re: [PATCH v2 26/30] vfio-pci/zdev: wire up zPCI adapter interrupt forwarding support

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 1/25/22 7:36 AM, Pierre Morel wrote:
> 
> 
> On 1/14/22 21:31, Matthew Rosato wrote:
>> Introduce support for VFIO_DEVICE_FEATURE_ZPCI_AIF, which is a new
>> VFIO_DEVICE_FEATURE ioctl.  This interface is used to indicate that an
>> s390x vfio-pci device wishes to enable/disable zPCI adapter interrupt
>> forwarding, which allows underlying firmware to deliver interrupts
>> directly to the associated kvm guest.
>>
>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_pci.h  |  2 +
>>   drivers/vfio/pci/vfio_pci_core.c |  2 +
>>   drivers/vfio/pci/vfio_pci_zdev.c | 98 +++++++++++++++++++++++++++++++-
>>   include/linux/vfio_pci_core.h    | 10 ++++
>>   include/uapi/linux/vfio.h        |  7 +++
>>   include/uapi/linux/vfio_zdev.h   | 20 +++++++
>>   6 files changed, 138 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_pci.h 
>> b/arch/s390/include/asm/kvm_pci.h
>> index dc00c3f27a00..dbab349a4a75 100644
>> --- a/arch/s390/include/asm/kvm_pci.h
>> +++ b/arch/s390/include/asm/kvm_pci.h
>> @@ -36,6 +36,8 @@ struct kvm_zdev {
>>       struct zpci_fib fib;
>>       struct notifier_block nb;
>>       bool interp;
>> +    bool aif;
>> +    bool fhost;
> 
> Can we please have a comment on these booleans? > Can we have explicit naming to be able to follow their usage more easily?
> May be aif_float and aif_host to match with the VFIO feature?

Sure, rename would be fine.

As for a comment, maybe something like

bool aif_float; /* Enabled for floating interrupt assist */
bool aif_host;  /* Require host delivery */

...

>> diff --git a/include/uapi/linux/vfio_zdev.h 
>> b/include/uapi/linux/vfio_zdev.h
>> index 575f0410dc66..c574e23f9385 100644
>> --- a/include/uapi/linux/vfio_zdev.h
>> +++ b/include/uapi/linux/vfio_zdev.h
>> @@ -90,4 +90,24 @@ struct vfio_device_zpci_interp {
>>       __u32 fh;        /* Host device function handle */
>>   };
>> +/**
>> + * VFIO_DEVICE_FEATURE_ZPCI_AIF
>> + *
>> + * This feature is used for enabling forwarding of adapter interrupts 
>> directly
>> + * from firmware to the guest.  When setting this feature, the flags 
>> indicate
>> + * whether to enable/disable the feature and the structure defined 
>> below is
>> + * used to setup the forwarding structures.  When getting this 
>> feature, only
>> + * the flags are used to indicate the current state.
>> + */
>> +struct vfio_device_zpci_aif {
>> +    __u64 flags;
>> +#define VFIO_DEVICE_ZPCI_FLAG_AIF_FLOAT 1
>> +#define VFIO_DEVICE_ZPCI_FLAG_AIF_HOST 2
> 
> I think we need more information on these flags.
> What does AIF_FLOAT and what does AIF_HOST ?
> 

You actually asked for this already on Jan 19 :), here's a copy of that 
response inline here:

I can add a small line comment for each, like:

  AIF_FLOAT 1 /* Floating interrupts enabled */
  AIF_HOST 2  /* Host delivery forced */

But here's a bit more detail:

On SET:
AIF_FLOAT = 1 means enable the interrupt forwarding assist for floating 
interrupt delivery
AIF_FLOAT = 0 means to disable it.
AIF_HOST = 1 means the assist will always deliver the interrupt to the 
host and let the host inject it
AIF_HOST = 0 host only gets interrupts when firmware can't deliver

on GET, we just indicate the current settings from the most recent SET, 
meaning:
AIF_FLOAT = 1 interrupt forwarding assist is currently active
AIF_FLOAT = 0 interrupt forwarding assist is not currently active
AIF_HOST = 1 interrupt forwarding will always go through host
AIF_HOST = 0 interrupt forwarding will only go through the host when 
necessary

My thought would be add the line comments in this patch and then the 
additional detail in a follow-on patch that adds vfio zPCI to 
Documentation/S390