Re: [PATCH 04/21] x86/mm/asi: set up asi_nonsensitive_pgd

[Borislav Petkov]

On Wed, Sep 24, 2025 at 02:59:39PM +0000, Brendan Jackman wrote:
> @@ -797,6 +800,24 @@ __kernel_physical_mapping_init(unsigned long paddr_start,
>  
>  	paddr_last = phys_pgd_init(init_mm.pgd, paddr_start, paddr_end, page_size_mask,
>  				   prot, init, &pgd_changed);
> +
> +	/*
> +	 * Set up ASI's unrestricted physmap. This needs to mapped at minimum 2M
> +	 * size so that regions can be mapped and unmapped at pageblock
> +	 * granularity without requiring allocations.
> +	 */
> +	if (asi_nonsensitive_pgd) {
> +		/*
> +		 * Since most memory is expected to end up sensitive, start with
> +		 * everything unmapped in this pagetable.
> +		 */
> +		pgprot_t prot_np = __pgprot(pgprot_val(prot) & ~_PAGE_PRESENT);
> +
> +		VM_BUG_ON((PAGE_SHIFT + pageblock_order) < page_level_shift(PG_LEVEL_2M));
> +		phys_pgd_init(asi_nonsensitive_pgd, paddr_start, paddr_end, 1 << PG_LEVEL_2M,
> +			      prot_np, init, NULL);
> +	}

This looks weird: so you have some other function - asi_init() - which *must*
run before this one so that the pgd is allocated. But then you check it here
and in order to do such a "distributed" init, you export it too.

Instead, I'd simply add a function call here - asi_init_physmap() or whatever
- which is defined in asi.c and gets *only* called from here. And that
function returns the pgd or NULL. And then you use phys_pgd_init() on it.

Also, looking at kernel_map_pages_in_pgd() - and you mentioned set_memory.c
already - and if I squint my eyes hard enough, it does look like a bunch of
redundancy between there and init_64.c. But that's nasty code so unifying that
would be a hard task.

Thx.

-- 
Regards/Gruss,
    Boris.

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