[Qemu-devel] [PATCH v1 4/5] s390x/pci: Refuse to realize VFIO-PCI if AIS needed but supported

[Pierre Morel]

In S390x the Adapter Interrupt Suppression facility is used to mask
interrupts of other PCI devices during interruption handling.

VFIO PCI allows the interrupts to be delivered rapidely through KVM via
IRQfd or to be delivered through QEMU.
The choice is made through the x-kvm-intx and x-kvo-misx properties of
the VFIO PCI device.

If the VFIO PCI device is using the direct KVM access through IRQfd and
we know that KVM does not implement AIS support we refuse to realize the
VFIO PCI device.

In all other cases, emulation and VFIO PCI sending interrupts through
QEMU, we intercept the propagated IRQ, and protect it with the QEMU AIS
implementation before to send it to the guest through KVM.

Signed-off-by: Pierre Morel <address@hidden>
---
 hw/s390x/s390-pci-bus.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index d9c294a..4afe49b 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -21,18 +21,21 @@
 #include "hw/pci/pci_bus.h"
 #include "hw/pci/pci_bridge.h"
 #include "hw/pci/msi.h"
+#include "hw/vfio/pci.h"
 #include "qemu/error-report.h"
 
 #ifndef DEBUG_S390PCI_BUS
 #define DEBUG_S390PCI_BUS  0
 #endif
 
+#ifndef DPRINTF
 #define DPRINTF(fmt, ...)                                         \
     do {                                                          \
         if (DEBUG_S390PCI_BUS) {                                  \
             fprintf(stderr, "S390pci-bus: " fmt, ## __VA_ARGS__); \
         }                                                         \
     } while (0)
+#endif
 
 S390pciState *s390_get_phb(void)
 {
@@ -751,6 +754,15 @@ static void s390_pcihost_hot_plug(HotplugHandler 
*hotplug_dev,
         }
 
         if (object_dynamic_cast(OBJECT(dev), "vfio-pci")) {
+            S390FLICState *fs = s390_get_flic();
+            VFIOPCIDevice *vdev = DO_UPCAST(VFIOPCIDevice, pdev, pdev);
+
+            if ((!vdev->no_kvm_msix || !vdev->no_kvm_msix) &&
+                (!fs || !fs->ais_supported)) {
+                error_setg(errp, "VFIO PCI is not supported "
+                           "because kernel has no AIS capability.");
+                return;
+            }
             pbdev->fh |= FH_SHM_VFIO;
         } else {
             pbdev->fh |= FH_SHM_EMUL;
-- 
2.3.0