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Re: [Xen-devel] [PATCH] VTD/Intremap: Disable Intremap on Chipset 5500/5520/X58 due to errata

On 16/01/13 13:57, Jan Beulich wrote:
On 16.01.13 at 00:27, Malcolm Crossley <malcolm.crossley@xxxxxxxxxx> wrote:

Stepping B-3 has two errata (#47 and #53) related to Interrupt
remapping, to which the workaround is for the BIOS to completely disable
interrupt remapping.  These errata are fixed in stepping C-2.

Unfortunately this chipset is very common and many BIOSes are not
disabling remapping.  We can detect this in Xen and prevent turning on
remapping in the first place.  However, this will turn VT-d off on many
systems by default.

Users who still wish to use VT-d can use iommu=force if they are happy
exposing the associated security risk.

Signed-off-by: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

diff -r 35a0556a7f76 -r ee475f0e6aeb xen/drivers/passthrough/vtd/quirks.c
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -244,6 +244,29 @@ void vtd_ops_postamble_quirk(struct iomm
+/* 5500/5520/X58 Chipset Interrupt remapping errata, for stepping B-3.
+ * Fixed in stepping C-2. */
+void __init tylersburg_intremap_quirk(void)
+    uint32_t bus, device;
+    uint8_t rev;
+    for ( bus = 0; bus < 0x100; bus++ )
+    {
+        /* Match on System Management Registers on Device 20 Function 0 */
+        device = pci_conf_read32(0, bus, 20, 0, PCI_VENDOR_ID);
+        rev = pci_conf_read8(0, bus, 20, 0, PCI_REVISION_ID);
+        if ( rev == 0x13 && device == 0x342e8086 )
+        {
+            dprintk(XENLOG_INFO VTDPREFIX,
+                    "Disabling Interrupt Remapping due to Intel 5500/5520/X58 
Chipset errata #47, #53\n");
+            iommu_intremap = 0;
Unless it is guaranteed that no system with this chipset can have
x2APIC, I don't think this is right. For one, this happens way too
late (namely after x2apic_bsp_setup()). And second, if you move
this earlier, such systems with x2APIC pre-enabled won't boot
After some digging, I discovered that the errata affects chipsets (5520,5500,X58) which don't have IOMMU EIM( Extended Interrupt Mode) support. EIM is required to support x2APIC mode and so this means the chipset can't support x2APIC mode and so we should never see a system with x2APIC enabled.

For reference, the chipset of this processor generation which does support EIM is the 7500 and it does not suffer from this errata.

Currently Xen is relying on the ACPI_DMAR_X2APIC_OPT_OUT bit in the DMAR table to detect x2apic support in the IOMMU. In theory it would be better to read the EIM bit in the IOMMU device itself instead of relying on the BIOS but this may be difficult to do at that early stage of initialisation of Xen.


+            break;
+        }
+    }
  /* initialize platform identification flags */
  void __init platform_quirks_init(void)
@@ -264,6 +287,9 @@ void __init platform_quirks_init(void)
/* ioremap IGD MMIO+0x2000 page */
+    /* Tylersburg interrupt remap quirk */
+    tylersburg_intremap_quirk();

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