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

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On 1/19/22 12:10 PM, Pierre Morel wrote:


On 1/14/22 21:31, Matthew Rosato wrote:
...
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

Generaly it looks good to me but I miss some explanation on these flags.

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


Which makes me realize that a more complete documentation under Documentation/S390 for VFIO zPCI as we have for VFIO AP and VFIO CCW would be of great interest.

You're not wrong -- a similar comment came up for QEMU. I will add this to my todo list as a follow-on.






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