# Re: \[PATCH v28 16/32\] x86/mm: Update maybe\_mkwrite() for shadow stack

- From: Borislav Petkov \<bp@alien8.de\>
- Date: 2021-08-16 17:03:36 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/08/1479479
- Thread: https://ratatoskr.run/linux-doc/2021/07/1455208/t.md

```text
On Thu, Jul 22, 2021 at 01:52:03PM -0700, Yu-cheng Yu wrote:
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 3364fe62b903..ba449d12ec32 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -610,6 +610,26 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
>  }
>  #endif
>  
> +pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> +{
> +	if (likely(vma->vm_flags & VM_WRITE))
> +		pte = pte_mkwrite(pte);
> +	else if (likely(vma->vm_flags & VM_SHADOW_STACK))
> +		pte = pte_mkwrite_shstk(pte);
> +	return pte;
> +}
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
> +{
> +	if (likely(vma->vm_flags & VM_WRITE))
> +		pmd = pmd_mkwrite(pmd);
> +	else if (likely(vma->vm_flags & VM_SHADOW_STACK))
> +		pmd = pmd_mkwrite_shstk(pmd);

What are all those likely()ies here for?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette
```