s390x/pci: enable for load/store interpretation

If the ZPCI_OP ioctl reports that is is available and usable, then the
underlying KVM host will enable load/store intepretation for any guest
device without a SHM bit in the guest function handle.  For a device that
will be using interpretation support, ensure the guest function handle
matches the host function handle; this value is re-checked every time the
guest issues a SET PCI FN to enable the guest device as it is the only
opportunity to reflect function handle changes.

By default, unless interpret=off is specified, interpretation support will
always be assumed and exploited if the necessary ioctl and features are
available on the host kernel.  When these are unavailable, we will silently
revert to the interception model; this allows existing guest configurations
to work unmodified on hosts with and without zPCI interpretation support,
allowing QEMU to choose the best support model available.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20220902172737.170349-4-mjrosato@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

1 files changed, 65 insertions, 1 deletions

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 4b2bdd94b3..156051e6e9 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -16,6 +16,7 @@
 #include "qapi/visitor.h"
 #include "hw/s390x/s390-pci-bus.h"
 #include "hw/s390x/s390-pci-inst.h"
+#include "hw/s390x/s390-pci-kvm.h"
 #include "hw/s390x/s390-pci-vfio.h"
 #include "hw/pci/pci_bus.h"
 #include "hw/qdev-properties.h"
@@ -971,12 +972,51 @@ static void s390_pci_update_subordinate(PCIDevice *dev, uint32_t nr)
     }
 }
 
+static int s390_pci_interp_plug(S390pciState *s, S390PCIBusDevice *pbdev)
+{
+    uint32_t idx, fh;
+
+    if (!s390_pci_get_host_fh(pbdev, &fh)) {
+        return -EPERM;
+    }
+
+    /*
+     * The host device is already in an enabled state, but we always present
+     * the initial device state to the guest as disabled (ZPCI_FS_DISABLED).
+     * Therefore, mask off the enable bit from the passthrough handle until
+     * the guest issues a CLP SET PCI FN later to enable the device.
+     */
+    pbdev->fh = fh & ~FH_MASK_ENABLE;
+
+    /* Next, see if the idx is already in-use */
+    idx = pbdev->fh & FH_MASK_INDEX;
+    if (pbdev->idx != idx) {
+        if (s390_pci_find_dev_by_idx(s, idx)) {
+            return -EINVAL;
+        }
+        /*
+         * Update the idx entry with the passed through idx
+         * If the relinquished idx is lower than next_idx, use it
+         * to replace next_idx
+         */
+        g_hash_table_remove(s->zpci_table, &pbdev->idx);
+        if (idx < s->next_idx) {
+            s->next_idx = idx;
+        }
+        pbdev->idx = idx;
+        g_hash_table_insert(s->zpci_table, &pbdev->idx, pbdev);
+    }
+
+    return 0;
+}
+
 static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                               Error **errp)
 {
     S390pciState *s = S390_PCI_HOST_BRIDGE(hotplug_dev);
     PCIDevice *pdev = NULL;
     S390PCIBusDevice *pbdev = NULL;
+    int rc;
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_BRIDGE)) {
         PCIBridge *pb = PCI_BRIDGE(dev);
@@ -1022,12 +1062,35 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
         set_pbdev_info(pbdev);
 
         if (object_dynamic_cast(OBJECT(dev), "vfio-pci")) {
-            pbdev->fh |= FH_SHM_VFIO;
+            /*
+             * By default, interpretation is always requested; if the available
+             * facilities indicate it is not available, fallback to the
+             * interception model.
+             */
+            if (pbdev->interp) {
+                if (s390_pci_kvm_interp_allowed()) {
+                    rc = s390_pci_interp_plug(s, pbdev);
+                    if (rc) {
+                        error_setg(errp, "Plug failed for zPCI device in "
+                                   "interpretation mode: %d", rc);
+                        return;
+                    }
+                } else {
+                    DPRINTF("zPCI interpretation facilities missing.\n");
+                    pbdev->interp = false;
+                }
+            }
             pbdev->iommu->dma_limit = s390_pci_start_dma_count(s, pbdev);
             /* Fill in CLP information passed via the vfio region */
             s390_pci_get_clp_info(pbdev);
+            if (!pbdev->interp) {
+                /* Do vfio passthrough but intercept for I/O */
+                pbdev->fh |= FH_SHM_VFIO;
+            }
         } else {
             pbdev->fh |= FH_SHM_EMUL;
+            /* Always intercept emulated devices */
+            pbdev->interp = false;
         }
 
         if (s390_pci_msix_init(pbdev)) {
@@ -1360,6 +1423,7 @@ static Property s390_pci_device_properties[] = {
     DEFINE_PROP_UINT16("uid", S390PCIBusDevice, uid, UID_UNDEFINED),
     DEFINE_PROP_S390_PCI_FID("fid", S390PCIBusDevice, fid),
     DEFINE_PROP_STRING("target", S390PCIBusDevice, target),
+    DEFINE_PROP_BOOL("interpret", S390PCIBusDevice, interp, true),
     DEFINE_PROP_END_OF_LIST(),
 };