From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f199.google.com (mail-qt0-f199.google.com [209.85.216.199]) by kanga.kvack.org (Postfix) with ESMTP id EB7F66B3246 for ; Fri, 24 Aug 2018 20:05:50 -0400 (EDT) Received: by mail-qt0-f199.google.com with SMTP id y54-v6so5297445qta.8 for ; Fri, 24 Aug 2018 17:05:50 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id d36-v6sor4370177qte.142.2018.08.24.17.05.50 for (Google Transport Security); Fri, 24 Aug 2018 17:05:50 -0700 (PDT) From: "Zi Yan" Subject: Re: [PATCH 4/7] mm/hmm: properly handle migration pmd Date: Fri, 24 Aug 2018 20:05:46 -0400 Message-ID: <0560A126-680A-4BAE-8303-F1AB34BE4BA5@cs.rutgers.edu> In-Reply-To: <20180824192549.30844-5-jglisse@redhat.com> References: <20180824192549.30844-1-jglisse@redhat.com> <20180824192549.30844-5-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=_MailMate_86A4A7E9-B661-45C6-8A35-BA7BDA284EA0_="; micalg=pgp-sha512; protocol="application/pgp-signature" Sender: owner-linux-mm@kvack.org List-ID: To: jglisse@redhat.com Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, "Aneesh Kumar K . V" , Ralph Campbell , John Hubbard This is an OpenPGP/MIME signed message (RFC 3156 and 4880). --=_MailMate_86A4A7E9-B661-45C6-8A35-BA7BDA284EA0_= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi J=C3=A9r=C3=B4me, On 24 Aug 2018, at 15:25, jglisse@redhat.com wrote: > From: J=C3=A9r=C3=B4me Glisse > > Before this patch migration pmd entry (!pmd_present()) would have > been treated as a bad entry (pmd_bad() returns true on migration > pmd entry). The outcome was that device driver would believe that > the range covered by the pmd was bad and would either SIGBUS or > simply kill all the device's threads (each device driver decide > how to react when the device tries to access poisonnous or invalid > range of memory). > > This patch explicitly handle the case of migration pmd entry which > are non present pmd entry and either wait for the migration to > finish or report empty range (when device is just trying to pre- > fill a range of virtual address and thus do not want to wait or > trigger page fault). > > Signed-off-by: Aneesh Kumar K.V > Signed-off-by: J=C3=A9r=C3=B4me Glisse > Cc: Ralph Campbell > Cc: John Hubbard > Cc: Andrew Morton > --- > mm/hmm.c | 45 +++++++++++++++++++++++++++++++++++++++------ > 1 file changed, 39 insertions(+), 6 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index a16678d08127..659efc9aada6 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -577,22 +577,47 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, > { > struct hmm_vma_walk *hmm_vma_walk =3D walk->private; > struct hmm_range *range =3D hmm_vma_walk->range; > + struct vm_area_struct *vma =3D walk->vma; > uint64_t *pfns =3D range->pfns; > unsigned long addr =3D start, i; > pte_t *ptep; > + pmd_t pmd; > > - i =3D (addr - range->start) >> PAGE_SHIFT; > > again: > - if (pmd_none(*pmdp)) > + pmd =3D READ_ONCE(*pmdp); > + if (pmd_none(pmd)) > return hmm_vma_walk_hole(start, end, walk); > > - if (pmd_huge(*pmdp) && (range->vma->vm_flags & VM_HUGETLB)) > + if (pmd_huge(pmd) && (range->vma->vm_flags & VM_HUGETLB)) > return hmm_pfns_bad(start, end, walk); > > - if (pmd_devmap(*pmdp) || pmd_trans_huge(*pmdp)) { > - pmd_t pmd; > + if (!pmd_present(pmd)) { > + swp_entry_t entry =3D pmd_to_swp_entry(pmd); > + > + if (is_migration_entry(entry)) { I think you should check thp_migration_supported() here, since PMD migrat= ion is only enabled in x86_64 systems. Other architectures should treat PMD migration entries as bad. > + bool fault, write_fault; > + unsigned long npages; > + uint64_t *pfns; > + > + i =3D (addr - range->start) >> PAGE_SHIFT; > + npages =3D (end - addr) >> PAGE_SHIFT; > + pfns =3D &range->pfns[i]; > + > + hmm_range_need_fault(hmm_vma_walk, pfns, npages, > + 0, &fault, &write_fault); > + if (fault || write_fault) { > + hmm_vma_walk->last =3D addr; > + pmd_migration_entry_wait(vma->vm_mm, pmdp); > + return -EAGAIN; > + } > + return 0; > + } > + > + return hmm_pfns_bad(start, end, walk); > + } > =E2=80=94 Best Regards, Yan Zi --=_MailMate_86A4A7E9-B661-45C6-8A35-BA7BDA284EA0_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQFKBAEBCgA0FiEEOXBxLIohamfZUwd5QYsvEZxOpswFAluAnVoWHHppLnlhbkBj cy5ydXRnZXJzLmVkdQAKCRBBiy8RnE6mzH0UCACrzspTKoppbPxVLBrUXSTqU8cT CiBGJx9CoWUt8BYW+5kV1Ih/vUhPOIWINrtCUecy6VVd1+7OrdoSiq+AZ+9a+XCK KXb/VKPv1r93iA8Mlo8E7DvwBYHMIBEjd35yUl4oJFkx4/6S7F0lCnyYRbi0sqDb jVBOziuebcscpU25YMDNyozOB6EVYsxv/nRO9E1wxD24ag4QWnPJcVsYOSHp/G5i Kk++tJcIZwMLAiNk2MlZqZ+QrjDszXNFPDy46UhcAYy0xvsodZyuFUvPM4w2LK3d yFSJrE72K1QU6vTxwAYJ1Zf5JvkX4U32L4POaw6yrnpw+JxpzOV74NBnVB/5 =J6/i -----END PGP SIGNATURE----- --=_MailMate_86A4A7E9-B661-45C6-8A35-BA7BDA284EA0_=--