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

Leizhen (ThunderTown)
2022-04-27T07:12:38Z

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