[PATCH for-4.15 2/4] xen/iommu: x86: Free the IOMMU page-tables with the pgtables.lock held

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

The pgtables.lock is protecting access to the page list pgtables.list.
However, iommu_free_pgtables() will not held it. I guess it was assumed
that page-tables cannot be allocated while the domain is dying.

Unfortunately, there is no guarantee that iommu_map() will not be
called while a domain is dying (it looks like to be possible from
XEN_DOMCTL_memory_mapping). So it would be possible to be concurrently
allocate memory and free the page-tables.

Therefore, we need to held the lock when freeing the page tables.

There are more issues around the IOMMU page-allocator. They will be
handled in follow-up patches.

Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 xen/drivers/passthrough/x86/iommu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xen/drivers/passthrough/x86/iommu.c 
b/xen/drivers/passthrough/x86/iommu.c
index cea1032b3d02..779dbb5b98ba 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -267,13 +267,18 @@ int iommu_free_pgtables(struct domain *d)
     struct page_info *pg;
     unsigned int done = 0;
 
+    spin_lock(&hd->arch.pgtables.lock);
     while ( (pg = page_list_remove_head(&hd->arch.pgtables.list)) )
     {
         free_domheap_page(pg);
 
         if ( !(++done & 0xff) && general_preempt_check() )
+        {
+            spin_unlock(&hd->arch.pgtables.lock);
             return -ERESTART;
+        }
     }
+    spin_unlock(&hd->arch.pgtables.lock);
 
     return 0;
 }
-- 
2.17.1