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Re: [Qemu-devel] [PATCH v1 4/5] s390x/pci: Refuse to realize VFIO-PCI if


From: Pierre Morel
Subject: Re: [Qemu-devel] [PATCH v1 4/5] s390x/pci: Refuse to realize VFIO-PCI if AIS needed but supported
Date: Mon, 9 Oct 2017 16:25:17 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0

On 09/10/2017 11:06, Cornelia Huck wrote:
On Wed,  4 Oct 2017 15:49:38 +0200
Pierre Morel <address@hidden> wrote:

"not supported", surely?
:)
yes, "not supported"


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

Ugh. Is there DPRINTF redefinition going on?

Yes in hw/vfio/vfio-common.h

But I think I better do an undef / def instead of a ifndef

#ifdef DPRINTF
#undef DPRINTF
#endif
#define DPRINTF(fmt, ...)
...




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) &&

One of the no_kvm_msix should probably be something else :)

:) yes

Historicaly, it used to be a no_kvm_intx but since AIS only works with AEN intx has no reason to be here.

So the second no_kvm_msix must disappear.


+                (!fs || !fs->ais_supported)) {
+                error_setg(errp, "VFIO PCI is not supported "
+                           "because kernel has no AIS capability.");

I think failure is per-device (i.e., you would be able to plug a
different vfio device if you turned off irqfd support for it); should
that be reflected in the error message?

OK, I will find something better.


+                return;
+            }

Would it make sense to fail plugging before we try to create a zpci
device?

clearly yes. I will put these test before the eventual zpci allocation.


              pbdev->fh |= FH_SHM_VFIO;
          } else {
              pbdev->fh |= FH_SHM_EMUL;



Thanks,

Pierre


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany




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