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Re: [PATCH v5 7/9] s390x/pci: enable adapter event notification for inte

From: Pierre Morel
Subject: Re: [PATCH v5 7/9] s390x/pci: enable adapter event notification for interpreted devices
Date: Mon, 2 May 2022 09:48:56 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0

On 4/22/22 14:10, Matthew Rosato wrote:
On 4/22/22 5:39 AM, Pierre Morel wrote:

On 4/4/22 20:17, Matthew Rosato wrote:
Use the associated kvm ioctl operation to enable adapter event notification
and forwarding for devices when requested.  This feature will be set up
with or without firmware assist based upon the 'forwarding_assist' setting.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
  hw/s390x/s390-pci-bus.c         | 20 ++++++++++++++---
  hw/s390x/s390-pci-inst.c        | 40 +++++++++++++++++++++++++++++++--
  hw/s390x/s390-pci-kvm.c         | 30 +++++++++++++++++++++++++
  include/hw/s390x/s390-pci-bus.h |  1 +
  include/hw/s390x/s390-pci-kvm.h | 14 ++++++++++++
  5 files changed, 100 insertions(+), 5 deletions(-)

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 9c02d31250..47918d2ce9 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -190,7 +190,10 @@ void s390_pci_sclp_deconfigure(SCCB *sccb)
-        if (pbdev->summary_ind) {
+        if (pbdev->interp && (pbdev->fh & FH_MASK_ENABLE)) {
+            /* Interpreted devices were using interrupt forwarding */
+            s390_pci_kvm_aif_disable(pbdev);

Same remark as for the kernel part.
The VFIO device is already initialized and the action is on this device, Shouldn't we use the VFIO device interface instead of the KVM interface?

I don't necessarily disagree, but in v3 of the kernel series I was told not to use VFIO ioctls to accomplish tasks that are unique to KVM (e.g. AEN interpretation) and to instead use a KVM ioctl.

VFIO_DEVICE_SET_IRQS won't work as-is for reasons described in the kernel series (e.g. we don't see any of the config space notifiers because of instruction interpretation) -- as far as I can figure we could add our own s390 code to QEMU to issue VFIO_DEVICE_SET_IRQS directly for an interpreted device, but I think would also need s390-specific changes to VFIO_DEVICE_SET_IRQS accommodate this (e.g. maybe something like a VFIO_IRQ_SET_DATA_S390AEN where we can then specify the aen information in vfio_irq_set.data -- or something else I


yes this in VFIO_DEVICE_SET_IRQS is what I think should be done.

haven't though of yet) -- I can try to look at this some more and see if I get a good idea.

I understood that the demand was concerning the IOMMU but I may be wrong.
For my opinion, the handling of AEN is not specific to KVM but specific to the device, for example the code should be the same if Z ever decide to use XEN or another hypervizor, except for the GISA part but this part is already implemented in KVM in a way it can be used from a device like in VFIO AP.

@Alex, what do you think?


Pierre Morel
IBM Lab Boeblingen

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