[Xen-devel] [PATCH] arm/p2m: Fix regression during domain shutdown with active mem_access

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

The change in commit 438c5fe4f0c introduced a regression for domains where
mem_acces is or was active. When relinquish_p2m_mapping attempts to clear
a page where the order is not 0 the following ASSERT is triggered:

    ASSERT(!p2m->mem_access_enabled || page_order == 0);

This regression was unfortunately not caught during testing in preparation
for the 4.8 release.

As at this point during domain shutdown it is safe to skip mem_access paths
altogether (pages are being relinquished), this patch flips the
mem_access_enabled flag to forgo any radix-tree lookups and to avoid
tripping the ASSERT.

Ideally this fix would be part of Xen 4.8.1.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/p2m.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 09ceb378a5..1f0ecc9970 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1376,6 +1376,9 @@ int relinquish_p2m_mapping(struct domain *d)
 
     p2m_write_lock(p2m);
 
+    /* No need for mem_access now */
+    p2m->mem_access_enabled = false;
+
     for ( ; gfn_x(start) < gfn_x(end);
           start = gfn_next_boundary(start, order) )
     {
-- 
2.11.0


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