[PATCH for-4.15 v5 1/3] xen/iommu: x86: Don't try to free page tables is the IOMMU is not enabled

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

When using CONFIG_BIGMEM=y, the page_list cannot be accessed whilst it
is is unitialized. However, iommu_free_pgtables() will be called even if
the domain is not using an IOMMU.

Consequently, Xen will try to go through the page list and deference a
NULL pointer.

Bail out early if the domain is not using an IOMMU.

Fixes: 15bc9a1ef51c ("x86/iommu: add common page-table allocator")
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

---
    Changes in v5:
        - Patch added. This was split from "xen/x86: iommu: Ignore
        IOMMU mapping requests when a domain is dying"
---
 xen/drivers/passthrough/x86/iommu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/drivers/passthrough/x86/iommu.c 
b/xen/drivers/passthrough/x86/iommu.c
index cea1032b3d02..58a330e82247 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -267,6 +267,9 @@ int iommu_free_pgtables(struct domain *d)
     struct page_info *pg;
     unsigned int done = 0;
 
+    if ( !is_iommu_enabled(d) )
+        return 0;
+
     while ( (pg = page_list_remove_head(&hd->arch.pgtables.list)) )
     {
         free_domheap_page(pg);
-- 
2.17.1