xen/debug: WARN_ON when identity PFN has no _PAGE_IOMAP flag set.

Only enabled if XEN_DEBUG is enabled. We print a warning
when:

 pfn_to_mfn(pfn) == pfn, but no VM_IO (_PAGE_IOMAP) flag set
	(and pfn is an identity mapped pfn)
 pfn_to_mfn(pfn) != pfn, and VM_IO flag is set.
	(ditto, pfn is an identity mapped pfn)

[v2: Make it dependent on CONFIG_XEN_DEBUG instead of ..DEBUG_FS]
[v3: Fix compiler warning]

Reviewed-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 5b54892e4bc3..e4343fe488ed 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -48,3 +48,11 @@ config XEN_DEBUG_FS
         help
           Enable statistics output and various tuning options in debugfs.
           Enabling this option may incur a significant performance overhead.
+
+config XEN_DEBUG
+        bool "Enable Xen debug checks"
+        depends on XEN
+        default n
+        help
+          Enable various WARN_ON checks in the Xen MMU code.
+          Enabling this option WILL incur a significant performance overhead.