x86: Make E820_X_MAX unconditionally larger than E820MAX

Alex Thorlton · jgross1 · commit 9d2f86c6cad5 · 2016-12-09T10:59:04.000+01:00
It's really not necessary to limit E820_X_MAX to 128 in the non-EFI
case.  This commit drops E820_X_MAX's dependency on CONFIG_EFI, so that
E820_X_MAX is always at least slightly larger than E820MAX.

The real motivation behind this is actually to prevent some issues in
the Xen kernel, where the XENMEM_machine_memory_map hypercall can
produce an e820 map larger than 128 entries, even on systems where the
original e820 table was quite a bit smaller than that, depending on how
many IOAPICs are installed on the system.

Signed-off-by: Alex Thorlton &lt;athorlton@sgi.com&gt;
Suggested-by: Ingo Molnar &lt;mingo@redhat.com&gt;
Acked-by: Ingo Molnar &lt;mingo@kernel.org&gt;
Signed-off-by: Juergen Gross &lt;jgross@suse.com&gt;
diff --git a/arch/x86/include/asm/e820.h b/arch/x86/include/asm/e820.h
@@ -1,13 +1,17 @@
 #ifndef _ASM_X86_E820_H
 #define _ASM_X86_E820_H
 
-#ifdef CONFIG_EFI
+/*
+ * E820_X_MAX is the maximum size of the extended E820 table.  The extended
+ * table may contain up to 3 extra E820 entries per possible NUMA node, so we
+ * make room for 3 * MAX_NUMNODES possible entries, beyond the standard 128.
+ * Also note that E820_X_MAX *must* be defined before we include uapi/asm/e820.h.
+ */
 #include <linux/numa.h>
 #define E820_X_MAX (E820MAX + 3 * MAX_NUMNODES)
-#else	/* ! CONFIG_EFI */
-#define E820_X_MAX E820MAX
-#endif
+
 #include <uapi/asm/e820.h>
+
 #ifndef __ASSEMBLY__
 /* see comment in arch/x86/kernel/e820.c */
 extern struct e820map *e820;
