From: Peter Xu <peterx@redhat.com>
To: Alistair Popple <apopple@nvidia.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Axel Rasmussen <axelrasmussen@google.com>,
Nadav Amit <nadav.amit@gmail.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Hugh Dickins <hughd@google.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Jerome Glisse <jglisse@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH v6 03/23] mm: Check against orig_pte for finish_fault()
Date: Thu, 16 Dec 2021 13:50:47 +0800 [thread overview]
Message-ID: <YbrTtx7gtOX+ZCia@xz-m1.local> (raw)
In-Reply-To: <YbrQ2bsEYsfHrIIV@xz-m1.local>
On Thu, Dec 16, 2021 at 01:38:33PM +0800, Peter Xu wrote:
> On Thu, Dec 16, 2021 at 04:01:47PM +1100, Alistair Popple wrote:
> > On Monday, 15 November 2021 6:55:02 PM AEDT Peter Xu wrote:
> > > We used to check against none pte and in those cases orig_pte should always be
> > > none pte anyway.
> >
> > Is that always true? From what I can see in handle_pte_fault() orig_pte only
> > gets initialised in the !pmd_none() case so might not be pte_none.
>
> I believe it's true, otherwise I must have overlooked.
>
> IMHO it's not "when we set orig_pte" that matters - note that finish_fault()
> (that this patch modifies) is only called for file-backed memories, and it's
> only called in do_fault() where the pte is not mapped at all.
>
> DAX seems to call it too, but still DAX comes from do_fault() too, afaict.
>
> The pte will not be mapped in two cases in handle_pte_fault():
>
> - When pmd_none
>
> - When !pmd_none, however if we find that pte_none==true, that's:
>
> if (pte_none(vmf->orig_pte)) {
> pte_unmap(vmf->pte);
> vmf->pte = NULL;
> }
>
> So when we're already in do_fault(), afaict, orig_pte must be pte_none().
> Another side note is that, IIUC pte_none() is a looser check than the
> pte_val()==0 and it should be arch dependent.
So one more thing I forgot to mention... Of course above is based on the fact
that orig_pte will be initialized to zero when creating vmf structure, and
that's done in __handle_mm_fault():
struct vm_fault vmf = {
.vma = vma,
.address = address & PAGE_MASK,
.flags = flags,
.pgoff = linear_page_index(vma, address),
.gfp_mask = __get_fault_gfp_mask(vma),
};
I'm not sure whether I should explicitly set it to pte_val(0), in most C
programs we'll already assume it's a proper reset of orig_pte value in c99
initialization format, but if anyone thinks we should do that explicitly plus
some comments I can do that too.
>
> Thanks,
>
> >
> > > This change prepares us to be able to call do_fault() on !none ptes. For
> > > example, we should allow that to happen for pte marker so that we can restore
> > > information out of the pte markers.
> > >
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > > mm/memory.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index 04662b010005..d5966d9e24c3 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > > @@ -4052,7 +4052,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
> > > vmf->address, &vmf->ptl);
> > > ret = 0;
> > > /* Re-check under ptl */
> > > - if (likely(pte_none(*vmf->pte)))
> > > + if (likely(pte_same(*vmf->pte, vmf->orig_pte)))
> > > do_set_pte(vmf, page, vmf->address);
> > > else
> > > ret = VM_FAULT_NOPAGE;
> > >
> >
> >
> >
> >
>
> --
> Peter Xu
--
Peter Xu
next prev parent reply other threads:[~2021-12-16 5:51 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-15 7:54 [PATCH v6 00/23] userfaultfd-wp: Support shmem and hugetlbfs Peter Xu
2021-11-15 7:55 ` [PATCH v6 01/23] mm: Introduce PTE_MARKER swap entry Peter Xu
2021-12-03 3:30 ` Alistair Popple
2021-12-03 4:21 ` Peter Xu
2021-12-03 5:35 ` Alistair Popple
2021-12-03 6:45 ` Peter Xu
2021-12-07 2:12 ` Alistair Popple
2021-12-07 2:30 ` Peter Xu
2021-11-15 7:55 ` [PATCH v6 02/23] mm: Teach core mm about pte markers Peter Xu
2021-11-15 7:55 ` [PATCH v6 03/23] mm: Check against orig_pte for finish_fault() Peter Xu
2021-12-16 5:01 ` Alistair Popple
2021-12-16 5:38 ` Peter Xu
2021-12-16 5:50 ` Peter Xu [this message]
2021-12-16 6:23 ` Alistair Popple
2021-12-16 7:06 ` Peter Xu
2021-12-16 7:45 ` Alistair Popple
2021-12-16 8:04 ` Peter Xu
2021-11-15 7:55 ` [PATCH v6 04/23] mm/uffd: PTE_MARKER_UFFD_WP Peter Xu
2021-12-16 5:18 ` Alistair Popple
2021-12-16 5:45 ` Peter Xu
2021-11-15 7:55 ` [PATCH v6 05/23] mm/shmem: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2021-11-15 7:55 ` [PATCH v6 06/23] mm/shmem: Handle uffd-wp special pte in page fault handler Peter Xu
2021-12-16 5:56 ` Alistair Popple
2021-12-16 6:17 ` Peter Xu
2021-12-16 6:30 ` Alistair Popple
2021-11-15 7:55 ` [PATCH v6 07/23] mm/shmem: Persist uffd-wp bit across zapping for file-backed Peter Xu
2021-11-15 8:00 ` [PATCH v6 08/23] mm/shmem: Allow uffd wr-protect none pte for file-backed mem Peter Xu
2021-11-15 8:00 ` [PATCH v6 09/23] mm/shmem: Allows file-back mem to be uffd wr-protected on thps Peter Xu
2021-11-15 8:01 ` [PATCH v6 10/23] mm/shmem: Handle uffd-wp during fork() Peter Xu
2021-11-15 8:01 ` [PATCH v6 11/23] mm/hugetlb: Introduce huge pte version of uffd-wp helpers Peter Xu
2021-11-15 8:01 ` [PATCH v6 12/23] mm/hugetlb: Hook page faults for uffd write protection Peter Xu
2021-11-15 8:01 ` [PATCH v6 13/23] mm/hugetlb: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2021-11-15 8:02 ` [PATCH v6 14/23] mm/hugetlb: Handle UFFDIO_WRITEPROTECT Peter Xu
2021-11-15 8:02 ` [PATCH v6 15/23] mm/hugetlb: Handle pte markers in page faults Peter Xu
2021-11-15 8:02 ` [PATCH v6 16/23] mm/hugetlb: Allow uffd wr-protect none ptes Peter Xu
2021-11-15 8:02 ` [PATCH v6 17/23] mm/hugetlb: Only drop uffd-wp special pte if required Peter Xu
2021-11-15 8:02 ` [PATCH v6 18/23] mm/hugetlb: Handle uffd-wp during fork() Peter Xu
2021-11-15 8:03 ` [PATCH v6 19/23] mm/khugepaged: Don't recycle vma pgtable if uffd-wp registered Peter Xu
2021-11-15 8:03 ` [PATCH v6 20/23] mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs Peter Xu
2021-11-15 8:03 ` [PATCH v6 21/23] mm/uffd: Enable write protection for shmem & hugetlbfs Peter Xu
2021-11-15 8:03 ` [PATCH v6 22/23] mm: Enable PTE markers by default Peter Xu
2021-11-15 8:04 ` [PATCH v6 23/23] selftests/uffd: Enable uffd-wp for shmem/hugetlbfs Peter Xu
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