Re: [PATCH v17 03/10] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel()

[Leizhen (ThunderTown)]

On 2021/12/16 9:10, Baoquan He wrote:
> On 12/15/21 at 02:28pm, Borislav Petkov wrote:
>> On Fri, Dec 10, 2021 at 02:55:26PM +0800, Zhen Lei wrote:
>>> @@ -518,7 +519,7 @@ static void __init reserve_crashkernel(void)
>>>  		}
>>>  	}
>>>  
>>> -	if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
>>> +	if (crash_base >= CRASH_ADDR_LOW_MAX && reserve_crashkernel_low()) {
>>>  		memblock_phys_free(crash_base, crash_size);
>>>  		return;
>>>  	}
>>
>> That's not a equivalent transformation on X86_32.

The original value (1ULL << 32) is inaccurate, and it enlarged the CRASH_ADDR_LOW
upper limit. This is because when the memory is allocated from the low end,
the address cannot exceed CRASH_ADDR_LOW_MAX, see "if (!high)" branch. If
the memory is allocated from the high end, 'crash_base' is greater than or
equal to (1ULL << 32), and naturally, it is greater than CRASH_ADDR_LOW_MAX.

I think I should update the description, thanks.

                if (!high)
                        crash_base = memblock_phys_alloc_range(crash_size,
                                                CRASH_ALIGN, CRASH_ALIGN,
                                                CRASH_ADDR_LOW_MAX);
                if (!crash_base)
                        crash_base = memblock_phys_alloc_range(crash_size,
                                                CRASH_ALIGN, CRASH_ALIGN,
                                                CRASH_ADDR_HIGH_MAX);

> 
> reserve_crashkernel_low() always return 0 on x86_32, so the not equivalent
> transformation for x86_32 doesn't matter, I think.
> 
> .
>