Re: [PATCH] x86/head/64: level2_kernel_pgt's kernel area is built with _PAGE_PRESENT set

Thomas Gleixner
2024-05-22T09:58:04Z

On Sat, Mar 23 2024 at 23:26, Wei Yang wrote:
> The code is first introduced in 'commit 1ab60e0f72f7 ("[PATCH] x86-64:
> Relocatable Kernel Support")'. Then 'commit c88d71508e36b
> ("x86/boot/64: Rewrite startup_64() in C")', convert it to c. And
> 'commit 2aa85f246c181 ("x86/boot/64: Make level2_kernel_pgt pages
> invalid outside kernel area")' limit the range from _text to _end.
>
> Originally, it does the check because the loop iterate the whole
> level2_kernel_pgt, while currently it just fixup the kernel area. This
> area is built with _PAGE_PRESENT set.

What's the actual problem you are trying to solve?

> /* fixup pages that are part of the kernel image */
> for (; i <= pmd_index((unsigned long)_end); i++)
> - if (pmd[i] & _PAGE_PRESENT)
> - pmd[i] += load_delta;
> + pmd[i] += load_delta;

Fixing up non-present PMDs is a pointless exercise.

Thanks,

tglx