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[PATCH 8/8] s390x/pci: Prevent ISM device passthrough on older host kern

From: Matthew Rosato
Subject: [PATCH 8/8] s390x/pci: Prevent ISM device passthrough on older host kernels
Date: Tue, 19 Jan 2021 15:44:19 -0500

If the underlying host does not provide CLP capabilities, we cannot tell
what type of function is being passed through, which means for ISM devices
we can't properly tell if the vfio I/O region is necessary.  If the ISM
device is allowed to pass through erroneously, it will not function
properly without the I/O region.  Therefore, check for unclassified devices
that do not have MSI-X support and still disallow these from being passed
through, using the same error as known ISM devices when the vfio I/O region
is unavailable.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
 hw/s390x/s390-pci-bus.c         | 13 +++++++++++++
 include/hw/s390x/s390-pci-bus.h |  1 +
 2 files changed, 14 insertions(+)

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 9d5c2c5..0dfdc88 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -1037,6 +1037,19 @@ static void s390_pcihost_plug(HotplugHandler 
*hotplug_dev, DeviceState *dev,
             if (pbdev->pft == ZPCI_PFT_ISM) {
                 ret = s390_pci_get_zpci_io_region(pbdev);
+            /*
+             * If the device type is unclassified, it may be due to the fact
+             * that CLP info was not provided by vfio -- Which means we cannot
+             * tell if this is actually an ISM device, which will not be able
+             * to function properly without proper identification and the I/O
+             * region.  Therefore, attempt to identify the ISM device via the
+             * lack of MSI-X and only in this case prevent the device from
+             * being passed through.
+             */
+            else if (pbdev->pft == ZPCI_PFT_UNCLASSIFIED &&
+                     !pci_find_capability(pbdev->pdev, PCI_CAP_ID_MSIX)) {
+                ret = -EINVAL;
+            }
             if (ret) {
                 error_setg(errp, "vfio zPCI I/O region support is mandatory "
                            "for %02x:%02x.%01x", pci_dev_bus_num(pdev),
diff --git a/include/hw/s390x/s390-pci-bus.h b/include/hw/s390x/s390-pci-bus.h
index aaef890..d75aad8 100644
--- a/include/hw/s390x/s390-pci-bus.h
+++ b/include/hw/s390x/s390-pci-bus.h
@@ -44,6 +44,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(S390PCIBusDevice, S390_PCI_DEVICE)
 /* PCI Function Types */
 #define ZPCI_PFT_ISM 5
 #define HP_EVENT_TO_CONFIGURED        0x0301

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