[Xen-devel] [PATCH for-4.13] passthrough: simplify locking and logging

Igor Druzhinin posted 1 patch 3 weeks ago
Failed in applying to current master (apply log)
xen/drivers/passthrough/pci.c | 101 ++++++++++++++++++------------------------
1 file changed, 42 insertions(+), 59 deletions(-)

[Xen-devel] [PATCH for-4.13] passthrough: simplify locking and logging

Posted by Igor Druzhinin 3 weeks ago
From: Paul Durrant <paul.durrant@citrix.com>

Dropping the pcidevs lock between calling device_assigned() and
assign_device() means that the latter has to do the same check as the
former for no obvious gain. Also, since long running operations under
pcidevs lock already drop the lock and return -ERESTART periodically there
is little point in immediately failing an assignment operation with
-ERESTART just because the pcidevs lock could not be acquired (for the
second time, having already blocked on acquiring the lock in
device_assigned()).

This patch instead acquires the lock once for assignment (or test assign)
operations directly in iommu_do_pci_domctl() and thus can remove the
duplicate domain ownership check in assign_device(). Whilst in the
neighbourhood, the patch also removes some debug logging from
assign_device() and deassign_device() and replaces it with proper error
logging, which allows error logging in iommu_do_pci_domctl() to be
removed. Also, since device_assigned() can tell the difference between a
guest assigned device and a non-existent one, log the actual error
condition rather then being ambiguous for the sake a few extra lines of
code.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
---

This is XSA-302 followup and contains some changes important for XenServer.
Juergen, could this be considered for 4.13 inclusion?

---
 xen/drivers/passthrough/pci.c | 101 ++++++++++++++++++------------------------
 1 file changed, 42 insertions(+), 59 deletions(-)

diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index e64666d..ea0770d 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -932,30 +932,27 @@ static int deassign_device(struct domain *d, uint16_t seg, uint8_t bus,
             break;
         ret = hd->platform_ops->reassign_device(d, target, devfn,
                                                 pci_to_dev(pdev));
-        if ( !ret )
-            continue;
-
-        printk(XENLOG_G_ERR "%pd: deassign %04x:%02x:%02x.%u failed (%d)\n",
-               d, seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn), ret);
-        return ret;
+        if ( ret )
+            goto out;
     }
 
     devfn = pdev->devfn;
     ret = hd->platform_ops->reassign_device(d, target, devfn,
                                             pci_to_dev(pdev));
     if ( ret )
-    {
-        dprintk(XENLOG_G_ERR,
-                "%pd: deassign device (%04x:%02x:%02x.%u) failed\n",
-                d, seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
-        return ret;
-    }
+        goto out;
 
     if ( pdev->domain == hardware_domain  )
         pdev->quarantine = false;
 
     pdev->fault.count = 0;
 
+out:
+    if ( ret )
+        printk(XENLOG_G_ERR
+               "%pd: deassign device (%04x:%02x:%02x.%u) failed (%d)\n", d,
+               seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn), ret);
+
     return ret;
 }
 
@@ -976,10 +973,7 @@ int pci_release_devices(struct domain *d)
     {
         bus = pdev->bus;
         devfn = pdev->devfn;
-        if ( deassign_device(d, pdev->seg, bus, devfn) )
-            printk("domain %d: deassign device (%04x:%02x:%02x.%u) failed!\n",
-                   d->domain_id, pdev->seg, bus,
-                   PCI_SLOT(devfn), PCI_FUNC(devfn));
+        deassign_device(d, pdev->seg, bus, devfn);
     }
     pcidevs_unlock();
 
@@ -1534,8 +1528,7 @@ static int device_assigned(u16 seg, u8 bus, u8 devfn)
     struct pci_dev *pdev;
     int rc = 0;
 
-    pcidevs_lock();
-
+    ASSERT(pcidevs_locked());
     pdev = pci_get_pdev(seg, bus, devfn);
 
     if ( !pdev )
@@ -1549,11 +1542,10 @@ static int device_assigned(u16 seg, u8 bus, u8 devfn)
               pdev->domain != dom_io )
         rc = -EBUSY;
 
-    pcidevs_unlock();
-
     return rc;
 }
 
+/* caller should hold the pcidevs_lock */
 static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
 {
     const struct domain_iommu *hd = dom_iommu(d);
@@ -1571,23 +1563,11 @@ static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
                   vm_event_check_ring(d->vm_event_paging)) )
         return -EXDEV;
 
-    if ( !pcidevs_trylock() )
-        return -ERESTART;
-
+    /* device_assigned() should already have cleared the device for assignment */
+    ASSERT(pcidevs_locked());
     pdev = pci_get_pdev(seg, bus, devfn);
-
-    rc = -ENODEV;
-    if ( !pdev )
-        goto done;
-
-    rc = 0;
-    if ( d == pdev->domain )
-        goto done;
-
-    rc = -EBUSY;
-    if ( pdev->domain != hardware_domain &&
-         pdev->domain != dom_io )
-        goto done;
+    ASSERT(pdev && (pdev->domain == hardware_domain ||
+                    pdev->domain == dom_io));
 
     if ( pdev->msix )
     {
@@ -1608,19 +1588,17 @@ static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
         if ( PCI_SLOT(devfn) != PCI_SLOT(pdev->devfn) )
             break;
         rc = hd->platform_ops->assign_device(d, devfn, pci_to_dev(pdev), flag);
-        if ( rc )
-            printk(XENLOG_G_WARNING "d%d: assign %04x:%02x:%02x.%u failed (%d)\n",
-                   d->domain_id, seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
-                   rc);
     }
 
  done:
+    if ( rc )
+        printk(XENLOG_G_ERR
+               "%pd: assign device (%04x:%02x:%02x.%u) failed (%d)\n", d,
+               seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn), rc);
     /* The device is assigned to dom_io so mark it as quarantined */
-    if ( !rc && d == dom_io )
+    else if ( d == dom_io )
         pdev->quarantine = true;
 
-    pcidevs_unlock();
-
     return rc;
 }
 
@@ -1776,29 +1754,40 @@ int iommu_do_pci_domctl(
         bus = PCI_BUS(machine_sbdf);
         devfn = PCI_DEVFN2(machine_sbdf);
 
+        pcidevs_lock();
         ret = device_assigned(seg, bus, devfn);
         if ( domctl->cmd == XEN_DOMCTL_test_assign_device )
         {
-            if ( ret )
+            switch ( ret )
             {
+            case 0:
+                break;
+
+            case -ENODEV:
                 printk(XENLOG_G_INFO
-                       "%04x:%02x:%02x.%u already assigned, or non-existent\n",
+                       "%04x:%02x:%02x.%u non-existent\n",
                        seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
                 ret = -EINVAL;
+                break;
+
+            case -EBUSY:
+                printk(XENLOG_G_INFO
+                       "%04x:%02x:%02x.%u already assigned\n",
+                       seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
+                ret = -EINVAL;
+                break;
+
+            default:
+                ret = -EINVAL;
+                break;
             }
-            break;
         }
-        if ( !ret )
+        else if ( !ret )
             ret = assign_device(d, seg, bus, devfn, flags);
+        pcidevs_unlock();
         if ( ret == -ERESTART )
             ret = hypercall_create_continuation(__HYPERVISOR_domctl,
                                                 "h", u_domctl);
-        else if ( ret )
-            printk(XENLOG_G_ERR
-                   "assign %04x:%02x:%02x.%u to dom%d failed (%d)\n",
-                   seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
-                   d->domain_id, ret);
-
         break;
 
     case XEN_DOMCTL_deassign_device:
@@ -1830,12 +1819,6 @@ int iommu_do_pci_domctl(
         pcidevs_lock();
         ret = deassign_device(d, seg, bus, devfn);
         pcidevs_unlock();
-        if ( ret )
-            printk(XENLOG_G_ERR
-                   "deassign %04x:%02x:%02x.%u from dom%d failed (%d)\n",
-                   seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
-                   d->domain_id, ret);
-
         break;
 
     default:
-- 
2.7.4


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