[RFC] arm64: early_ioremap fails to map ACPI MADT on 64K pages

[Will Deacon]

On Tue, Jun 23, 2026 at 10:47:12AM +0800, Yu Peng wrote:
> Hi Lorenzo, Hanjun, Will,
> 
> Thanks for confirming.
> 
> I will send a proper patch for this. The change I plan to post is along
> these lines:
> 
> diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
> index ... .. ...
> --- a/arch/arm64/include/asm/fixmap.h
> +++ b/arch/arm64/include/asm/fixmap.h
> @@ -79,7 +79,11 @@ enum fixed_addresses {
>  	 * Temporary boot-time mappings, used by early_ioremap(),
>  	 * before ioremap() is functional.
>  	 */
> +#ifdef CONFIG_ARM64_64K_PAGES
> +#define NR_FIX_BTMAPS		(SZ_512K / PAGE_SIZE)
> +#else
>  #define NR_FIX_BTMAPS		(SZ_256K / PAGE_SIZE)
> +#endif
>  #define FIX_BTMAPS_SLOTS	7
>  #define TOTAL_FIX_BTMAPS	(NR_FIX_BTMAPS * FIX_BTMAPS_SLOTS)

I still don't understand why this issue is specific to 64k pages, though.

In the example you gave, the thing wasn't even 4k aligned.

Will