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

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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@xxxxxxxxxxxxx>
---
  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




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