[PATCH RFC] ARM: mm: Fix for highmem on machines with more than 14 cores

[PATCH RFC] ARM: mm: Fix for highmem on machines with more than 14 cores

[Anders Berg]

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

[PATCH RFC] ARM: mm: Fix for highmem on machines with more than 14 cores

[Anders Berg]

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).

Signed-off-by: Anders Berg <anders.berg@lsi.com>
Signed-off-by: Fredrik Markström <fredrik.markstrom@gmail.com>
---
 arch/arm/include/asm/fixmap.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index bbae919..40f1f05 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -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

Re: [PATCH RFC] ARM: mm: Fix for highmem on machines with more than 14 cores

[Nicolas Pitre]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 546 bytes --]

On Mon, 24 Mar 2014, Anders Berg wrote:

> 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).
> 
> Signed-off-by: Anders Berg <anders.berg@lsi.com>
> Signed-off-by: Fredrik Markström <fredrik.markstrom@gmail.com>

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

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


Nicolas