[PATCH] Allow Hypervisor build with more than 64 CPUs

[PATCH] Allow Hypervisor build with more than 64 CPUs

[Bill Burns]

Trying to build the Xen hypervisor with max_phys_cpus=128
for x86_64 fails. (Note that this was on a 3.1 base, but
unstable appears to have the same issue).

There is a build assertion due to the size of
the page_info structure and the shadow_page_info
structures get out of sync due to the presence
of cpumask_t in the page info structure (which
grows with more than 64 CPUs).

The proposed fix is to tack on the following to
the end of shadow_page_info structure.

Kudo's to Eduardo Habkost for the workaround.

Signed-off-by: Bill Burns <bburns@redhat.com>


--- xen/arch/x86/mm/shadow/private.h.orig	2007-12-06 12:48:38.000000000 -0500
+++ xen/arch/x86/mm/shadow/private.h	2008-08-12 12:52:49.000000000 -0400
@@ -243,6 +243,12 @@ struct shadow_page_info
         /* For non-pinnable shadows, a higher entry that points at us */
         paddr_t up;
     };
+#if NR_CPUS > 64
+    /* Need to add some padding to match struct page_info size,
+    * if cpumask_t is larger than a long
+    */
+    u8 padding[sizeof(cpumask_t)-sizeof(long)];
+#endif
 };

Re: [PATCH] Allow Hypervisor build with more than 64 CPUs

[Keir Fraser]

On 15/8/08 20:26, "Bill Burns" <bburns@redhat.com> wrote:

> Trying to build the Xen hypervisor with max_phys_cpus=128
> for x86_64 fails. (Note that this was on a 3.1 base, but
> unstable appears to have the same issue).
> 
> There is a build assertion due to the size of
> the page_info structure and the shadow_page_info
> structures get out of sync due to the presence
> of cpumask_t in the page info structure (which
> grows with more than 64 CPUs).
> 
> The proposed fix is to tack on the following to
> the end of shadow_page_info structure.

This should be fixed in c/s 18324 by relaxing the BUILD_BUG_ON().

 -- Keir