[PATCH] The patch solves the type error of the parameter âoffâ in syscall mmap on the ARM64 platform.

From: Boyang Zhou
Date: Wed Apr 17 2019 - 08:38:22 EST

The error information is that âoffset value too large for defined data typeâ.
On the X86 platform, the data type of âoff" is unsigned long; but on the ARM64 platform, the data type is defined as off_t, and off_t is by type long instead of unsigned long.
When the off right shifts in the function âsys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT)"on ARM64, high address of off is filled with sign bit 1instead of 0.
In our case, we mmap GPU doorbell on both platform. On the x86 platform, the value of off is f009c00000000000, after shift the value becomes f009c00000000; while on the ARM64, the value of off changes from ed35c00000000000 to fffed35c00000000. This value is treated as unsigned long in later functions. So it is too big for off and the error happened.
We have tested the patchs in Huawei ARM64 server with a couples of AMD GPUs.

Signed-off-by: Boyang Zhou <zhouby_cn@xxxxxxx>
arch/arm64/kernel/sys.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/sys.c b/arch/arm64/kernel/sys.c
index b44065f..6f91e81 100644
--- a/arch/arm64/kernel/sys.c
+++ b/arch/arm64/kernel/sys.c
@@ -31,7 +31,7 @@

SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len,
unsigned long, prot, unsigned long, flags,
- unsigned long, fd, off_t, off)
+ unsigned long, fd, unsigned long, off)
if (offset_in_page(off) != 0)
return -EINVAL;