[PATCH RFC] mips: bootmem: Don't use memory holes for page bitmap

[PATCH RFC] mips: bootmem: Don't use memory holes for page bitmap

[Alexander Sverdlin]

Commit f9a7febd leads to a fact that mapstart and therefore a page bitmap for
bootmem allocator immediately follows initrd_end. This doesn't always work
well on Octeon, where there are holes in PFN ranges (refer to 5b3b1688 and
4MB-aligned PFN allocation). Depending on the inird location it could happen,
that mapstart would be in an area not allocated by plat_mem_setup() in
arch/mips/cavium-octeon/setup.c, but in the alignment hole between initrd and
the next PFN area. Later on this memory will be unconditionally made available
to buddy allocator at the end of free_all_bootmem_core() (mm/bootmem.c).
All of this results in Linux using the memory not designated for Linux in
Octeon's plat_mem_setup(), which in turn means corruption of the memory used
by another OS/baremetal code on the same SoC.

It doesn't look to me as a problem of Octeon platform code, but rather as an
inability of f9a7febd to deal correctly with the fragmented memory-mappings.
Proposed fix moves the check for initrd address to the same calculation-loop
in bootmem_init() (arch/mips/kernel/setup.c), which also accounts for kernel
code location. This should result in mapstart located starting from the first
PFN area after kernel code AND initrd.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
---

Tested on CN63xx (Octeon2) -based HW.

 arch/mips/kernel/setup.c |   13 +++++--------
 1 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index be73c49..008b337 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -337,6 +337,11 @@ static void __init bootmem_init(void)
 			min_low_pfn = start;
 		if (end <= reserved_end)
 			continue;
+#ifdef CONFIG_BLK_DEV_INITRD
+		/* mapstart should be after initrd_end */
+		if (initrd_end && end <= (unsigned long)PFN_UP(__pa(initrd_end)))
+			continue;
+#endif
 		if (start >= mapstart)
 			continue;
 		mapstart = max(reserved_end, start);
@@ -366,14 +371,6 @@ static void __init bootmem_init(void)
 		max_low_pfn = PFN_DOWN(HIGHMEM_START);
 	}
 
-#ifdef CONFIG_BLK_DEV_INITRD
-	/*
-	 * mapstart should be after initrd_end
-	 */
-	if (initrd_end)
-		mapstart = max(mapstart, (unsigned long)PFN_UP(__pa(initrd_end)));
-#endif
-
 	/*
 	 * Initialize the boot-time allocator with low memory only.
 	 */

Re: [PATCH RFC] mips: bootmem: Don't use memory holes for page bitmap

[Ralf Baechle]

On Thu, Jul 02, 2015 at 05:16:01PM +0200, Alexander Sverdlin wrote:

> Commit f9a7febd leads to a fact that mapstart and therefore a page bitmap for
> bootmem allocator immediately follows initrd_end. This doesn't always work
> well on Octeon, where there are holes in PFN ranges (refer to 5b3b1688 and
> 4MB-aligned PFN allocation). Depending on the inird location it could happen,
> that mapstart would be in an area not allocated by plat_mem_setup() in
> arch/mips/cavium-octeon/setup.c, but in the alignment hole between initrd and
> the next PFN area. Later on this memory will be unconditionally made available
> to buddy allocator at the end of free_all_bootmem_core() (mm/bootmem.c).
> All of this results in Linux using the memory not designated for Linux in
> Octeon's plat_mem_setup(), which in turn means corruption of the memory used
> by another OS/baremetal code on the same SoC.
> 
> It doesn't look to me as a problem of Octeon platform code, but rather as an
> inability of f9a7febd to deal correctly with the fragmented memory-mappings.
> Proposed fix moves the check for initrd address to the same calculation-loop
> in bootmem_init() (arch/mips/kernel/setup.c), which also accounts for kernel
> code location. This should result in mapstart located starting from the first
> PFN area after kernel code AND initrd.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>

Appears reasonable.  Applied.

Thanks,

  Ralf