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[Xen-devel] [PATCH for-4.12 v2 4/7] pvh/dom0: warn when dom0_mem is not set

There have been several reports of the dom0 builder running out of
memory when building a PVH dom0 without having specified a dom0_mem
value. Print a warning message if dom0_mem is not set when booting in
PVH mode.

This is a temporary workaround until accounting for internal memory
required by Xen (ie: paging structures) is improved.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Without this patch creating a PVH dom0 without a dom0_mem parameter
can result in the dom0 builder running out of memory thus leading to a
Xen crash. The added message gives a hit to the user about a possible
Changes since v1:
 - Rewrite the warning message.
 - Check nr_pages in order to figure out if the amount of dom0 memory
   has been set.
 xen/arch/x86/dom0_build.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index 2b4d9e9ea6..95d60d1163 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -378,8 +378,18 @@ unsigned long __init dom0_compute_nr_pages(
          * maximum of 128MB.
         if ( !nr_pages )
+        {
             nr_pages = avail - (pv_shim ? pv_shim_mem(avail)
                                  : min(avail / 16, 128UL << (20 - 
+            if ( is_hvm_domain(d) )
+                /*
+                 * Temporary workaround message until internal (paging) memory
+                 * accounting required to build a pvh dom0 is improved.
+                 */
+                printk("WARNING: PVH dom0 without dom0_mem set is still 
unstable. "
+                       "If you get crashes during boot, try adding a dom0_mem 
+        }
         /* Clamp according to min/max limits and available memory. */
         nr_pages = max(nr_pages, min_pages);

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