From 8909691b6c5a84b67573b23ee8bb917b005628f0 Mon Sep 17 00:00:00 2001 From: David Hildenbrand <david@redhat.com> Date: Mon, 9 May 2022 18:20:44 -0700 Subject: [PATCH] mm/gup: disallow follow_page(FOLL_PIN) We want to change the way we handle R/O pins on anonymous pages that might be shared: if we detect a possibly shared anonymous page -- mapped R/O and not !PageAnonExclusive() -- we want to trigger unsharing via a page fault, resulting in an exclusive anonymous page that can be pinned reliably without getting replaced via COW on the next write fault. However, the required page fault will be problematic for follow_page(): in contrast to ordinary GUP, follow_page() doesn't trigger faults internally. So we would have to end up failing a R/O pin via follow_page(), although there is something mapped R/O into the page table, which might be rather surprising. We don't seem to have follow_page(FOLL_PIN) users, and it's a purely internal MM function. Let's just make our life easier and the semantics of follow_page() clearer by just disallowing FOLL_PIN for follow_page() completely. Link: https://lkml.kernel.org/r/20220428083441.37290-15-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/gup.c | 3 +++ mm/hugetlb.c | 8 +++++--- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index f598a037eb04f..f424abf5e7925 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -787,6 +787,9 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, if (vma_is_secretmem(vma)) return NULL; + if (foll_flags & FOLL_PIN) + return NULL; + page = follow_page_mask(vma, address, foll_flags, &ctx); if (ctx.pgmap) put_dev_pagemap(ctx.pgmap); diff --git a/mm/hugetlb.c b/mm/hugetlb.c index c0012b4a8eec1..e0308a44ba16a 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6719,9 +6719,11 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, spinlock_t *ptl; pte_t pte; - /* FOLL_GET and FOLL_PIN are mutually exclusive. */ - if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == - (FOLL_PIN | FOLL_GET))) + /* + * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via + * follow_hugetlb_page(). + */ + if (WARN_ON_ONCE(flags & FOLL_PIN)) return NULL; retry: