Re: [PATCH] x86/e820: set end to (start + size - 1) in __append_e820_map()

[Wei Yang <richard.weiyang@gmail.com>]

Hi, All,

Is my understanding correct?

On Sat, Aug 20, 2016 at 01:40:13AM +0000, Wei Yang wrote:
>The (start, size) tuple represents a range [start, start + size - 1],
>which means "start" and "start + size - 1" should be compared to see
>whether the range overflows.
>
>For example, a range with (start, size)
>
>	(0xffffffff fffffff0, 0x00000000 00000010)
>
>represents
>
>	[0xffffffff fffffff0, 0xffffffff ffffffff]
>
>would be judged overflow in the original code, while actually it is not.
>
>This patch fixes this and makes sure it still works when size is zero.
>
>Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>---
> arch/x86/kernel/e820.c |    4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
>index 621b501..871f186 100644
>--- a/arch/x86/kernel/e820.c
>+++ b/arch/x86/kernel/e820.c
>@@ -388,11 +388,11 @@ static int __init __append_e820_map(struct e820entry *biosmap, int nr_map)
> 	while (nr_map) {
> 		u64 start = biosmap->addr;
> 		u64 size = biosmap->size;
>-		u64 end = start + size;
>+		u64 end = start + size - 1;
> 		u32 type = biosmap->type;
> 
> 		/* Overflow in 64 bits? Ignore the memory map. */
>-		if (start > end)
>+		if (start > end && likely(size))
> 			return -1;
> 
> 		e820_add_region(start, size, type);
>-- 
>1.7.9.5

-- 
Wei Yang
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