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[2003:cb:c705:6d00:5870:9639:1c17:8162]) by smtp.gmail.com with ESMTPSA id y15-20020adfee0f000000b002c3efca57e1sm10530708wrn.110.2023.02.13.03.44.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Feb 2023 03:44:57 -0800 (PST) Message-ID: Date: Mon, 13 Feb 2023 12:44:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH] mm/userfaultfd: Support operation on multiple VMAs To: Muhammad Usama Anjum , peterx@redhat.com, Andrew Morton Cc: kernel@collabora.com, Paul Gofman , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230213104323.1792839-1-usama.anjum@collabora.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230213104323.1792839-1-usama.anjum@collabora.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4843780004 X-Stat-Signature: pc395rxr76prbpri3wu984wdeis76rmk X-Rspam-User: X-HE-Tag: 1676288701-360103 X-HE-Meta: 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 mlzsSpGP 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 13.02.23 11:43, Muhammad Usama Anjum wrote: > mwriteprotect_range() errors out if [start, end) doesn't fall in one > VMA. We are facing a use case where multiple VMAs are present in one > range of interest. For example, the following pseudocode reproduces the > error which we are trying to fix: > > - Allocate memory of size 16 pages with PROT_NONE with mmap > - Register userfaultfd > - Change protection of the first half (1 to 8 pages) of memory to > PROT_READ | PROT_WRITE. This breaks the memory area in two VMAs. > - Now UFFDIO_WRITEPROTECT_MODE_WP on the whole memory of 16 pages errors > out. > > This is a simple use case where user may or may not know if the memory > area has been divided into multiple VMAs. > > Reported-by: Paul Gofman > Signed-off-by: Muhammad Usama Anjum > --- > mm/userfaultfd.c | 36 +++++++++++++++++++----------------- > 1 file changed, 19 insertions(+), 17 deletions(-) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 65ad172add27..46e0a014af68 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -738,9 +738,11 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start, > unsigned long len, bool enable_wp, > atomic_t *mmap_changing) > { > + unsigned long end = start + len; > struct vm_area_struct *dst_vma; > unsigned long page_mask; > int err; > + VMA_ITERATOR(vmi, dst_mm, start); > > /* > * Sanitize the command parameters: > @@ -762,26 +764,26 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start, > if (mmap_changing && atomic_read(mmap_changing)) > goto out_unlock; > > - err = -ENOENT; > - dst_vma = find_dst_vma(dst_mm, start, len); > - > - if (!dst_vma) > - goto out_unlock; > - if (!userfaultfd_wp(dst_vma)) > - goto out_unlock; > - if (!vma_can_userfault(dst_vma, dst_vma->vm_flags)) > - goto out_unlock; > + for_each_vma_range(vmi, dst_vma, end) { > + err = -ENOENT; > > - if (is_vm_hugetlb_page(dst_vma)) { > - err = -EINVAL; > - page_mask = vma_kernel_pagesize(dst_vma) - 1; > - if ((start & page_mask) || (len & page_mask)) > - goto out_unlock; > - } > + if (!dst_vma->vm_userfaultfd_ctx.ctx) > + break; > + if (!userfaultfd_wp(dst_vma)) > + break; > + if (!vma_can_userfault(dst_vma, dst_vma->vm_flags)) > + break; > > - uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp); > + if (is_vm_hugetlb_page(dst_vma)) { > + err = -EINVAL; > + page_mask = vma_kernel_pagesize(dst_vma) - 1; > + if ((start & page_mask) || (len & page_mask)) > + break; > + } > > - err = 0; > + uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp); I suspect you should be adjusting the range to only cover that specific VMA here. -- Thanks, David / dhildenb