Re: [PATCH v2 1/2] x86/boot/64: Make level2_kernel_pgt pages invalid outside kernel area.

[Dave Hansen]

On 9/23/19 11:15 AM, Steve Wahl wrote:
>  	pmd = fixup_pointer(level2_kernel_pgt, physaddr);
> -	for (i = 0; i < PTRS_PER_PMD; i++) {
> +	for (i = 0; i < pmd_index((unsigned long)_text); i++)
> +		pmd[i] &= ~_PAGE_PRESENT;
> +
> +	for (; i <= pmd_index((unsigned long)_end); i++)
>  		if (pmd[i] & _PAGE_PRESENT)
>  			pmd[i] += load_delta;
> -	}
> +
> +	for (; i < PTRS_PER_PMD; i++)
> +		pmd[i] &= ~_PAGE_PRESENT;

This is looking a bunch better.  The broken-up loop could probably use
some comments, or you could combine it back to a single loop like this:

	int text_start_pmd_index = pmd_index((unsigned long)_text);
	int text_end_pmd_index   = pmd_index((unsigned long)_end);

	for (i = 0; i < PTRS_PER_PMD; i++) {
		if ((i < text_start_pmd_index) ||
		    (i > text_end_pmd_index)) {
			/* Unmap entries not mapping the kernel image */
			pmd[i] &= ~_PAGE_PRESENT;
		} else if (pmd[i] & _PAGE_PRESENT)
 			pmd[i] += load_delta;
		}
	}

Although I'd prefer it get commented or rewritten, it's passable like
this, so:

Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>