Re: [Xen-devel] [PATCH] cleanup for __start_xen()

[Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>]

Keir Fraser wrote:
> On 30/11/2009 17:42, "Ian Jackson" <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> 
>> I wrote:
>>> Xiao Guangrong writes ("[Xen-devel] [PATCH] cleanup for __start_xen()"):
>>>> -        if ( !initial_images_start && (s < e) &&
>>>> +        if ( !initial_images_start &&
>>> This is wrong.  s and e are uint64_t so if !(s < e), (e-s) will be
>>> large and positive.
>> I see this has already been applied (20523).  It should be reverted, I
>> think.
> 
> None of the if() blocks in the loop will make e<s, as that would imply that
> the block had allocated itself a chunk of memory that starts below s. So it
> is actually safe to remove the checks, as we know e>=s. But now I look at it
> I think I broke the module-relocation block some time ago -- it ends up with
> 'e' being too large by modules_headroom. :-( Will look into that more
> tomorrow...
> 

I thinks remove this judgment is very safe, because we have judge it at the 
begin of this loop:

for ( i = boot_e820.nr_map-1; i >= 0; i-- )
    {
        uint64_t s, e, mask = (1UL << L2_PAGETABLE_SHIFT) - 1;
        
        <snip>

        if ( (boot_e820.map[i].type != E820_RAM) || (s >= e) )  /* NOTICE HERE*/
            continue;
        
        /* it must s < e while run below code, not need check it again ... */
        ......
}

Thanks,
Xiao

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