qemu: hostdev: Add checks if PCI passthrough is available in the host

Add code to check availability of PCI passhthrough using VFIO and the
legacy KVM passthrough and use it when starting VMs and hotplugging
devices to live machine.

src/qemu/qemu_hostdev.c

@@ -23,6 +23,11 @@
 
 #include <config.h>
 
+#include <dirent.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <errno.h>
+
 #include "qemu_hostdev.h"
 #include "virlog.h"
 #include "virerror.h"
@@ -31,6 +36,7 @@
 #include "virusb.h"
 #include "virscsi.h"
 #include "virnetdev.h"
+#include "virfile.h"
 
 #define VIR_FROM_THIS VIR_FROM_QEMU
 
@@ -486,6 +492,122 @@ qemuDomainHostdevNetConfigRestore(virDomainHostdevDefPtr hostdev,
 }
 
 
+static bool
+qemuHostdevHostSupportsPassthroughVFIO(void)
+{
+    DIR *iommuDir = NULL;
+    struct dirent *iommuGroup = NULL;
+    bool ret = false;
+
+    /* condition 1 - /sys/kernel/iommu_groups/ contains entries */
+    if (!(iommuDir = opendir("/sys/kernel/iommu_groups/")))
+        goto cleanup;
+
+    while ((iommuGroup = readdir(iommuDir))) {
+        /* skip ./ ../ */
+        if (STRPREFIX(iommuGroup->d_name, "."))
+            continue;
+
+        /* assume we found a group */
+        break;
+    }
+
+    if (!iommuGroup)
+        goto cleanup;
+    /* okay, iommu is on and recognizes groups */
+
+    /* condition 2 - /dev/vfio/vfio exists */
+    if (!virFileExists("/dev/vfio/vfio"))
+        goto cleanup;
+
+    ret = true;
+
+cleanup:
+    if (iommuDir)
+        closedir(iommuDir);
+
+    return ret;
+}
+
+
+#if HAVE_LINUX_KVM_H
+# include <linux/kvm.h>
+static bool
+qemuHostdevHostSupportsPassthroughLegacy(void)
+{
+    int kvmfd = -1;
+    bool ret = false;
+
+    if ((kvmfd = open("/dev/kvm", O_RDONLY)) < 0)
+        goto cleanup;
+
+# ifdef KVM_CAP_IOMMU
+    if ((ioctl(kvmfd, KVM_CHECK_EXTENSION, KVM_CAP_IOMMU)) <= 0)
+        goto cleanup;
+
+    ret = true;
+# endif
+
+cleanup:
+    VIR_FORCE_CLOSE(kvmfd);
+
+    return ret;
+}
+#else
+static bool
+qemuHostdevHostSupportsPassthroughLegacy(void)
+{
+    return false;
+}
+#endif
+
+
+static bool
+qemuPrepareHostdevPCICheckSupport(virDomainHostdevDefPtr *hostdevs,
+                                  size_t nhostdevs)
+{
+    bool supportsPassthroughKVM = qemuHostdevHostSupportsPassthroughLegacy();
+    bool supportsPassthroughVFIO = qemuHostdevHostSupportsPassthroughVFIO();
+    size_t i;
+
+    /* assign defaults for hostdev passthrough */
+    for (i = 0; i < nhostdevs; i++) {
+        virDomainHostdevDefPtr hostdev = hostdevs[i];
+        int *backend = &hostdev->source.subsys.u.pci.backend;
+
+        if (hostdev->mode != VIR_DOMAIN_HOSTDEV_MODE_SUBSYS)
+            continue;
+        if (hostdev->source.subsys.type != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_PCI)
+            continue;
+
+        switch ((virDomainHostdevSubsysPciBackendType) *backend) {
+        case VIR_DOMAIN_HOSTDEV_PCI_BACKEND_VFIO:
+            if (!supportsPassthroughVFIO) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("host doesn't support VFIO PCI passthrough"));
+                return false;
+            }
+            break;
+
+        case VIR_DOMAIN_HOSTDEV_PCI_BACKEND_DEFAULT:
+        case VIR_DOMAIN_HOSTDEV_PCI_BACKEND_KVM:
+            if (!supportsPassthroughKVM) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("host doesn't support legacy PCI passthrough"));
+                return false;
+            }
+
+            break;
+
+        case VIR_DOMAIN_HOSTDEV_PCI_BACKEND_TYPE_LAST:
+            break;
+        }
+    }
+
+    return true;
+}
+
+
 int
 qemuPrepareHostdevPCIDevices(virQEMUDriverPtr driver,
                              const char *name,
@@ -499,6 +621,9 @@ qemuPrepareHostdevPCIDevices(virQEMUDriverPtr driver,
     int ret = -1;
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
 
+    if (!qemuPrepareHostdevPCICheckSupport(hostdevs, nhostdevs))
+        goto cleanup;
+
     virObjectLock(driver->activePciHostdevs);
     virObjectLock(driver->inactivePciHostdevs);