Re: [PATCH] x86/mm: Define the zapped-entry checks only with CONFIG_DEBUG_VM

[Dave Hansen]

On 11/2/26 06:39, Kiryl Shutsemau (Meta) wrote:
...
> +#ifdef CONFIG_DEBUG_VM
>  void arch_check_zapped_pte(struct vm_area_struct *vma, pte_t pte)
>  {
>  	/*
> @@ -823,3 +824,4 @@ void arch_check_zapped_pud(struct vm_area_struct *vma, pud_t pud)
>  	/* See note in arch_check_zapped_pte() */
>  	VM_WARN_ON_ONCE(!(vma->vm_flags & VM_SHADOW_STACK) && pud_shstk(pud));
>  }
> +#endif

So all these #ifdefs are because VM_SHADOW_STACK, a *constant* is not
available? That's unfortunate.

I dislike doing this gunk with macros, but I'd take that over new
#ifdefs. Or, settle the "does the arch provide these debug functions?"
at Kconfig time with an ARCH_HAS_FOO option. That could even be driven
from the x86 side with:

	select ARCH_HAS_CHECK_ZAPPED_PTE if DEBUG_VM

Or, put them in a new header. They're only used in memory.c, so what's
keeping them in pgtable.h? Another header could reference
VM_SHADOW_STACK. No?

Or, heck, I'm not that attached to these checks. Let's just kill them.

But I really don't like the new #ifdefs. It would be about my fifth
favorite way to fix this.