linux-kernel - Re: [PATCH v2 7/9] mm/memory: factor out common code from vm_normal_page

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Message-ID: <50190a14-78fb-4a4a-82fa-d7b887aa4754@lucifer.local>
Date: Thu, 17 Jul 2025 20:55:43 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        xen-devel@...ts.xenproject.org, linux-fsdevel@...r.kernel.org,
        nvdimm@...ts.linux.dev, Andrew Morton <akpm@...ux-foundation.org>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
        Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        Hugh Dickins <hughd@...gle.com>, Oscar Salvador <osalvador@...e.de>,
        Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v2 7/9] mm/memory: factor out common code from
 vm_normal_page_*()

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 :)

Anyway, again it'd be nice to somehow find a way to separate the special
check out from the rest.