[PATCH] amd iommu: Fix a xen crash after pci-attach

[Wei Wang2 <wei.wang2@amd.com>]

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Keir,
pci-detach triggers IO page table deallocation if the last passthru device has 
been removed from pdev list, and this will result a BUG on amd systems for 
next pci-attach. This patch fixes this issue.
Thanks,
Wei

Signed-off-by: Wei Wang <wei.wang2@amd.com>
--
Advanced Micro Devices GmbH
Sitz: Dornach, Gemeinde Aschheim, 
Landkreis München Registergericht München, 
HRB Nr. 43632
WEEE-Reg-Nr: DE 12919551
Geschäftsführer:
Alberto Bozzo, Andrew Bowd

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diff -r a69965e61ae9 xen/drivers/passthrough/amd/pci_amd_iommu.c
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c	Mon Jan 31 17:47:24 2011 +0000
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c	Tue Feb 01 17:19:16 2011 +0100
@@ -301,6 +301,11 @@ static int reassign_device( struct domai
     if ( target->max_pages > 0 )
         t->paging_mode = get_paging_mode(target->max_pages);
 
+    /* IO page tables might be destroyed after pci-detach the last device
+     * In this case, we have to re-allocate root table for next pci-attach.*/
+    if ( t->root_table == NULL )
+        allocate_domain_resources(t);
+
     amd_iommu_setup_domain_device(target, iommu, bdf);
     AMD_IOMMU_DEBUG("Re-assign %02x:%02x.%x from domain %d to domain %d\n",
                     bus, PCI_SLOT(devfn), PCI_FUNC(devfn),

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