Re: [PATCH v2 7/9] mm/memory: factor out common code from vm_normal_page_*()

[David Hildenbrand]

On 17.07.25 21:55, Lorenzo Stoakes wrote:
> On Thu, Jul 17, 2025 at 08:51:51PM +0100, Lorenzo Stoakes wrote:
> > > @@ -721,37 +772,21 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
> > >   		print_bad_page_map(vma, addr, pmd_val(pmd), NULL);
> > >   		return NULL;
> > >   	}
> > > -
> > > -	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
> > > -		if (vma->vm_flags & VM_MIXEDMAP) {
> > > -			if (!pfn_valid(pfn))
> > > -				return NULL;
> > > -			goto out;
> > > -		} else {
> > > -			unsigned long off;
> > > -			off = (addr - vma->vm_start) >> PAGE_SHIFT;
> > > -			if (pfn == vma->vm_pgoff + off)
> > > -				return NULL;
> > > -			if (!is_cow_mapping(vma->vm_flags))
> > > -				return NULL;
> > > -		}
> > > -	}
> > > -
> > > -	if (is_huge_zero_pfn(pfn))
> > > -		return NULL;
> > > -	if (unlikely(pfn > highest_memmap_pfn)) {
> > > -		print_bad_page_map(vma, addr, pmd_val(pmd), NULL);
> > > -		return NULL;
> > > -	}
> > > -
> > > -	/*
> > > -	 * NOTE! We still have PageReserved() pages in the page tables.
> > > -	 * eg. VDSO mappings can cause them to exist.
> > > -	 */
> > > -out:
> > > -	return pfn_to_page(pfn);
> > > +	return vm_normal_page_pfn(vma, addr, pfn, pmd_val(pmd));
> >
> > Hmm this seems broken, because you're now making these special on arches with
> > pte_special() right? But then you're invoking the not-special function?
> >
> > Also for non-pte_special() arches you're kind of implying they _maybe_ could be
> > special.
>
> OK sorry the diff caught me out here, you explicitly handle the pmd_special()
> case here, duplicatively (yuck).
>
> Maybe you fix this up in a later patch :)

I had that, but the conditions depend on the level, meaning: unnecessary 
checks for pte/pmd/pud level.

I had a variant where I would pass "bool special" into 
vm_normal_page_pfn(), but I didn't like it.

To optimize out, I would have to provide a "level" argument, and did not 
convince myself yet that that is a good idea at this point.

--
Cheers,

David / dhildenb