From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id 496006B4CD0 for ; Wed, 29 Aug 2018 13:18:01 -0400 (EDT) Received: by mail-qt0-f197.google.com with SMTP id b5-v6so5252150qtk.4 for ; Wed, 29 Aug 2018 10:18:01 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id k6-v6si1369104qke.96.2018.08.29.10.18.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 29 Aug 2018 10:18:00 -0700 (PDT) From: jglisse@redhat.com Subject: [PATCH 4/7] mm/hmm: properly handle migration pmd v2 Date: Wed, 29 Aug 2018 13:17:49 -0400 Message-Id: <20180829171749.9365-1-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 In-Reply-To: <20180824192549.30844-5-jglisse@redhat.com> Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: Andrew Morton , linux-kernel@vger.kernel.org, =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , "Aneesh Kumar K . V" , Zi Yan , Michal Hocko , Ralph Campbell , John Hubbard From: JA(C)rA'me 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). Changed since v1: - use is_pmd_migration_entry() instead of open coding the equivalent. Signed-off-by: Aneesh Kumar K.V Signed-off-by: JA(C)rA'me Glisse Cc: Zi Yan Cc: Michal Hocko Cc: Ralph Campbell Cc: John Hubbard Cc: Andrew Morton --- mm/hmm.c | 42 ++++++++++++++++++++++++++++++++++++------ 1 file changed, 36 insertions(+), 6 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index a16678d08127..fd3d19d98070 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -577,22 +577,44 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, { struct hmm_vma_walk *hmm_vma_walk = walk->private; struct hmm_range *range = hmm_vma_walk->range; + struct vm_area_struct *vma = walk->vma; uint64_t *pfns = range->pfns; unsigned long addr = start, i; pte_t *ptep; + pmd_t pmd; - i = (addr - range->start) >> PAGE_SHIFT; again: - if (pmd_none(*pmdp)) + pmd = 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 (is_pmd_migration_entry(pmd)) { + swp_entry_t entry = pmd_to_swp_entry(pmd); + + bool fault, write_fault; + unsigned long npages; + uint64_t *pfns; + + i = (addr - range->start) >> PAGE_SHIFT; + npages = (end - addr) >> PAGE_SHIFT; + pfns = &range->pfns[i]; + hmm_range_need_fault(hmm_vma_walk, pfns, npages, + 0, &fault, &write_fault); + if (fault || write_fault) { + hmm_vma_walk->last = addr; + pmd_migration_entry_wait(vma->vm_mm, pmdp); + return -EAGAIN; + } + return 0; + } else if (!pmd_present(pmd)) + return hmm_pfns_bad(start, end, walk); + + if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) { /* * No need to take pmd_lock here, even if some other threads * is splitting the huge pmd we will get that event through @@ -607,13 +629,21 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd)) goto again; + i = (addr - range->start) >> PAGE_SHIFT; return hmm_vma_handle_pmd(walk, addr, end, &pfns[i], pmd); } - if (pmd_bad(*pmdp)) + /* + * We have handled all the valid case above ie either none, migration, + * huge or transparent huge. At this point either it is a valid pmd + * entry pointing to pte directory or it is a bad pmd that will not + * recover. + */ + if (pmd_bad(pmd)) return hmm_pfns_bad(start, end, walk); ptep = pte_offset_map(pmdp, addr); + i = (addr - range->start) >> PAGE_SHIFT; for (; addr < end; addr += PAGE_SIZE, ptep++, i++) { int r; -- 2.17.1