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Re: [Xen-devel] [PATCH v3] AMD/intremap: Prevent use of per-device vector maps until irq logic is fixed

On 6/27/2013 3:47 AM, Jan Beulich wrote:
On 27.06.13 at 01:28, Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx>
On 6/26/2013 4:54 AM, Andrew Cooper wrote:
On 04/06/13 17:38, Andrew Cooper wrote:
XSA-36 changed the default vector map mode from global to per-device.  This is
because a global vector map does not prevent one PCI device from
another and launching a DoS on the system.

However, the per-device vector map logic is broken for devices with multiple
MSI-X vectors, which can either result in a failed ASSERT() or misprogramming
of a guests interrupt remapping tables.  The core problem is not trivial to

In an effort to get AMD systems back to a non-regressed state, introduce a
type of vector map called per-device-global.  This uses per-device vector maps
in the IOMMU, but uses a single used_vector map for the core IRQ logic.

This patch is intended to be removed as soon as the per-device logic is fixed

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Can we get a decision on this?  The 4.3 is looming and multi MSI-X PCI
functions are *still* broken on AMD systems, in all stable versions of
Xen, regressed by XSA-36.

  From my understanding of the points so far, we have agreed that this
patch is suitable for 4.3 and previous, with Jan's multi-MSI series
being the correct solution going forwards into 4.4.
Since the feedback suggesting that cleaning up is probably not
necessary, the only thing is probably the use of the word "BUG". Could
it be replaced with "Workaround" instead?
I'd just drop the "BUG:". And I can certainly do so while applying.
So in cases where you want something trivial changed, you could
simply give an ack saying under what conditions that ack applies.

Acked with removing the word "BUG" as suggested by Jan.


The only query at the moment is for the exact wording, which has had no
attention for a week.


Changes since v2:
   * Do not override command line.

Changes since v1:
   * Correct stupid mistake in commit message, making it confusing to read

diff -r 2d37d2d652a8 -r a017d74f346d
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -223,8 +223,19 @@ int __init amd_iov_detect(void)
           if ( amd_iommu_perdev_intremap )
-            printk("AMD-Vi: Enabling per-device vector maps\n");
-            opt_irq_vector_map = OPT_IRQ_VECTOR_MAP_PERDEV;
+            /* Per-device vector map logic is broken for devices with
+             * MSI-X interrupts (and would also be for multiple MSI, if Xen
+             * supported it).
+             *
+             * Until this is fixed, use global vector tables as far as the
+             * logic is concerned to avoid the buggy behaviour of per-device
+             * maps in map_domain_pirq(), and use per-device tables as far
+             * intremap code is concerned to avoid the security issue.
+             */
+            printk(XENLOG_WARNING "AMD-Vi BUG: per-device vector map logic is
broken.  "
+                   "Using per-device-global maps instead until a fix is
+            opt_irq_vector_map = OPT_IRQ_VECTOR_MAP_GLOBAL;
@@ -235,6 +246,12 @@ int __init amd_iov_detect(void)
           printk("AMD-Vi: Not overriding irq_vector_map setting\n");
+        if ( opt_irq_vector_map != OPT_IRQ_VECTOR_MAP_GLOBAL )
+        {
+            printk(XENLOG_WARNING "AMD-Vi BUG: per-device vector map logic is
broken.  "
+                   "Use irq_vector_map=global to work around.");
+        }
       if ( !amd_iommu_perdev_intremap )
           printk(XENLOG_WARNING "AMD-Vi: Using global interrupt remap table
is not recommended (see XSA-36)!\n");
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