Re: [PATCH v22 4/9] arm64: kdump: Don't force page-level mappings for memory above 4G

[Leizhen (ThunderTown)]

On 2022/4/26 22:26, Catalin Marinas wrote:
> On Thu, Apr 14, 2022 at 07:57:15PM +0800, Zhen Lei wrote:
>> @@ -540,13 +540,31 @@ static void __init map_mem(pgd_t *pgdp)
>>  	for_each_mem_range(i, &start, &end) {
>>  		if (start >= end)
>>  			break;
>> +
>> +#ifdef CONFIG_KEXEC_CORE
>> +		if (eflags && (end >= SZ_4G)) {
>> +			/*
>> +			 * The memory block cross the 4G boundary.
>> +			 * Forcibly use page-level mappings for memory under 4G.
>> +			 */
>> +			if (start < SZ_4G) {
>> +				__map_memblock(pgdp, start, SZ_4G - 1,
>> +					       pgprot_tagged(PAGE_KERNEL), flags | eflags);
>> +				start  = SZ_4G;
>> +			}
>> +
>> +			/* Page-level mappings is not mandatory for memory above 4G */
>> +			eflags = 0;
>> +		}
>> +#endif
> 
> That's a bit tricky if a SoC has all RAM above 4G. IIRC AMD Seattle had
> this layout. See max_zone_phys() for how we deal with this, basically
> extending ZONE_DMA to the whole range if RAM starts above 4GB. In that
> case, crashkernel reservation would fall in the range above 4GB.
> 
> BTW, we changed the max_zone_phys() logic with commit 791ab8b2e3db
> ("arm64: Ignore any DMA offsets in the max_zone_phys() calculation").

Okay, thanks for your correction. I'll dig into it after I've done the original requirement.

> 

-- 
Regards,
  Zhen Lei