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Subject[PATCH v2 RESEND 2/2] x86/mm/KASLR: Do not adapt the size of the direct mapping section for SGI UV system
On SGI UV system, kernel often hangs when KASLR is enabled. Disabling
KASLR makes kernel work well.

The back trace is:

kernel BUG at arch/x86/mm/init_64.c:311!
invalid opcode: 0000 [#1] SMP
RIP: 0010:__init_extra_mapping+0x188/0x196
Call Trace:
? rest_init+0x80/0x80

This is because the SGI UV system need map its MMIOH region to the direct
mapping section, and the mapping happens in rest_init() which is much
later than the calling of kernel_randomize_memory() to do mm KASLR. So
mm KASLR can't count in the size of the MMIOH region when caculate the
needed size of address space for the direct mapping section.

When KASLR is disabled, there are 64TB address space for both system RAM
and the MMIOH regions to share. When KASLR is enabled, the current code
of mm KASLR only reserves the actual size of system RAM plus extra 10TB
for the direct mapping. Thus later the MMIOH mapping could go beyond
the upper bound of the direct mapping to step into VMALLOC or VMEMMAP area.
Then BUG_ON() in __init_extra_mapping() will be triggered.

E.g on the SGI UV3 machine where this bug is reported , there are two MMIOH

[ 1.519001] UV: Map MMIOH0_HI 0xffc00000000 - 0x100000000000
[ 1.523001] UV: Map MMIOH1_HI 0x100000000000 - 0x200000000000

They are [16TB-16G, 16TB) and [16TB, 32TB). On this machine, 512G RAM are
spread out to 1TB regions. Then above two SGI MMIOH regions also will be
mapped into the direct mapping section.

To fix it, we need check if it's SGI UV system by calling is_early_uv_system()
in kernel_randomize_memory(). If yes, do not adapt the size of the direct
mapping section, just keep it as 64TB.

Signed-off-by: Baoquan He <>
Reviewed-by: Thomas Garnier <>
Acked-by: Mike Travis <>
Cc: Ingo Molnar <>
Cc: "H. Peter Anvin" <>
Cc: Thomas Garnier <>
Cc: Kees Cook <>
Cc: Andrew Morton <>
Cc: Masahiro Yamada <>
arch/x86/mm/kaslr.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index af599167fe3c..4d68c08df82d 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -27,6 +27,7 @@
#include <asm/pgtable.h>
#include <asm/setup.h>
#include <asm/kaslr.h>
+#include <asm/uv/uv.h>

#include "mm_internal.h"

@@ -123,7 +124,7 @@ void __init kernel_randomize_memory(void)

/* Adapt phyiscal memory region size based on available memory */
- if (memory_tb < kaslr_regions[0].size_tb)
+ if (memory_tb < kaslr_regions[0].size_tb && !is_early_uv_system())
kaslr_regions[0].size_tb = memory_tb;

/* Calculate entropy available between regions */
 \ /
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