On Tue, Jun 17, 2025 at 11:49:20AM +0200, David Hildenbrand wrote:
> On 16.06.25 13:58, Alistair Popple wrote:
> > Nothing uses PFN_DEV anymore so no need to create devmap pXd's when
> > mapping a PFN. Instead special mappings will be created which ensures
> > vm_normal_page_pXd() will not return pages which don't have an
> > associated page. This could change behaviour slightly on architectures
> > where pXd_devmap() does not imply pXd_special() as the normal page
> > checks would have fallen through to checking VM_PFNMAP/MIXEDMAP instead,
> > which in theory at least could have returned a page.
> >
> > However vm_normal_page_pXd() should never have been returning pages for
> > pXd_devmap() entries anyway, so anything relying on that would have been
> > a bug.
> >
> > Signed-off-by: Alistair Popple <apopple@nvidia.com>
> >
> > ---
> >
> > Changes since v1:
> >
> > - New for v2
> > ---
> > mm/huge_memory.c | 12 ++----------
> > 1 file changed, 2 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index b096240..6514e25 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1415,11 +1415,7 @@ static int insert_pmd(struct vm_area_struct *vma, unsigned long addr,
> > add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
> > } else {
> > entry = pmd_mkhuge(pfn_t_pmd(fop.pfn, prot));
> > -
> > - if (pfn_t_devmap(fop.pfn))
> > - entry = pmd_mkdevmap(entry);
> > - else
> > - entry = pmd_mkspecial(entry);
> > + entry = pmd_mkspecial(entry);
> > }
> > if (write) {
> > entry = pmd_mkyoung(pmd_mkdirty(entry));
> > @@ -1565,11 +1561,7 @@ static void insert_pud(struct vm_area_struct *vma, unsigned long addr,
> > add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR);
> > } else {
> > entry = pud_mkhuge(pfn_t_pud(fop.pfn, prot));
> > -
> > - if (pfn_t_devmap(fop.pfn))
> > - entry = pud_mkdevmap(entry);
> > - else
> > - entry = pud_mkspecial(entry);
> > + entry = pud_mkspecial(entry);
> > }
> > if (write) {
> > entry = pud_mkyoung(pud_mkdirty(entry));
>
>
> Why not squash this patch into #3, and remove the pmd_special() check from
> vm_normal_page_pmd() in the same go? Seems wrong to handle the PMD/PUD case
> separately.
Yeah, that was mostly because "someone" (and thankyou btw, it was somewhat my
mess) changed all this while I was working on it :-) I wanted to make the rebase
fixups obvious but will squash them for v3.
> But now I am confused why some pte_devmap() checks are removed in patch #3,
> while others are removed in #7.
>
> Why not split it up into (a) stop setting p*_devmap() and (b) remove
> p*_devmap().
>
> Logically makes more sense to me ... :)
Heh. You're right. For various reasons this patch series has gone through a
couple of reorderings, mainly to get rid of unused stuff early in the series but
that didn't work out due to that RISC-V bug. I needed a break from silly rebase
build errors so this was a good checkpoint.
But I've reworked things for v3 to get the ordering a bit more sensible.
> --
> Cheers,
>
> David / dhildenb
>