ARM: mm: Fix for highmem on machines with more than 14 cores

Hi,

While working of platform support for the LSI AXM5516 SoC (a 16 x A15 device) we ran into this limitation in fixmap.h where there is not enough room for the per-cpu pages if NR_CPUS is set to 16.

The following patch avoids the overlap by lowering the base address according to the values of NR_CPUS and KM_TYPE_NR. Is this the way to handle this?

Thanks,
Anders

Anders Berg (1):
ARM: mm: Fix for highmem on machines with more than 14 cores

 arch/arm/include/asm/fixmap.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

1.8.3.2

The fixmap area was hard coded to 224 pages which was only enough for 14 CPU:s. Now the area adapts to the configured number of CPU:s (NR_CPUS). We still have a hard limit of 30 CPU:s since we only have a single pte-chunk (512 pte:s).

---
 arch/arm/include/asm/fixmap.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

index bbae919..40f1f05 100644
@@ -7,15 +7,15 @@
  * On ARM we already have well known fixed virtual addresses imposed by
  * the architecture such as the vector page which is located at 0xffff0000,
  * therefore a second level page table is already allocated covering
- * 0xfff00000 upwards.
+ * 0xffe00000 upwards.
  *
  * The cache flushing code in proc-xscale.S uses the virtual area between
  * 0xfffe0000 and 0xfffeffff.
  */
 
-#define FIXADDR_START		0xfff00000UL
+#define FIXADDR_SIZE		((KM_TYPE_NR * NR_CPUS) << PAGE_SHIFT)
 #define FIXADDR_TOP		0xfffe0000UL
-#define FIXADDR_SIZE		(FIXADDR_TOP - FIXADDR_START)
+#define FIXADDR_START		(FIXADDR_TOP - FIXADDR_SIZE)
 
 #define FIX_KMAP_BEGIN		0
 #define FIX_KMAP_END		(FIXADDR_SIZE >> PAGE_SHIFT)

1.8.3.2

This is under discussion already. Please have a look at this thread:

http://news.gmane.org/group/gmane.linux.kernel/thread=1672068/

Nicolas