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Message-ID: <371b8fdd-129d-4fe3-bbc7-f0a1bc433b30@redhat.com> Date: Fri, 30 May 2025 11:37:21 +0200 From: David Hildenbrand <david@...hat.com> To: Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org Cc: gerald.schaefer@...ux.ibm.com, dan.j.williams@...el.com, jgg@...pe.ca, willy@...radead.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de, zhang.lyra@...il.com, debug@...osinc.com, bjorn@...nel.org, balbirs@...dia.com, lorenzo.stoakes@...cle.com, linux-arm-kernel@...ts.infradead.org, loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org, linux-cxl@...r.kernel.org, dri-devel@...ts.freedesktop.org, John@...ves.net Subject: Re: [PATCH 02/12] mm: Convert pXd_devmap checks to vma_is_dax On 29.05.25 08:32, Alistair Popple wrote: > Currently dax is the only user of pmd and pud mapped ZONE_DEVICE > pages. Therefore page walkers that want to exclude DAX pages can check > pmd_devmap or pud_devmap. However soon dax will no longer set PFN_DEV, > meaning dax pages are mapped as normal pages. > > Ensure page walkers that currently use pXd_devmap to skip DAX pages > continue to do so by adding explicit checks of the VMA instead. > > Signed-off-by: Alistair Popple <apopple@...dia.com> > --- > fs/userfaultfd.c | 2 +- > mm/hmm.c | 2 +- > mm/userfaultfd.c | 2 +- > 3 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 22f4bf9..de671d3 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -304,7 +304,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, > goto out; > > ret = false; > - if (!pmd_present(_pmd) || pmd_devmap(_pmd)) > + if (!pmd_present(_pmd) || vma_is_dax(vmf->vma)) > goto out; > > if (pmd_trans_huge(_pmd)) { > diff --git a/mm/hmm.c b/mm/hmm.c > index 082f7b7..db12c0a 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -429,7 +429,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > return hmm_vma_walk_hole(start, end, -1, walk); > } > > - if (pud_leaf(pud) && pud_devmap(pud)) { > + if (pud_leaf(pud) && vma_is_dax(walk->vma)) { > unsigned long i, npages, pfn; > unsigned int required_fault; > unsigned long *hmm_pfns; > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index e0db855..133f750 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -1791,7 +1791,7 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, > > ptl = pmd_trans_huge_lock(src_pmd, src_vma); > if (ptl) { > - if (pmd_devmap(*src_pmd)) { > + if (vma_is_dax(src_vma)) { > spin_unlock(ptl); > err = -ENOENT; > break; I assume we could also just refuse dax folios, right? If we decide to check VMAs, we should probably check earlier. But I wonder, what about anonymous non-dax pages in COW mappings? Is it possible? Not supported? If supported, checking the actual folio would be the right thing to do. -- Cheers, David / dhildenb
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