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[2003:cb:c74d:6400:4867:4ed0:9726:a0c9]) by smtp.gmail.com with ESMTPSA id r12-20020adff10c000000b0033de2f2a88dsm20096450wro.103.2024.03.07.02.52.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Mar 2024 02:52:18 -0800 (PST) Message-ID: Date: Thu, 7 Mar 2024 11:52:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] [RFC] proc: pagemap: Expose whether a PTE is writable To: Richard Weinberger , linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, upstream+pagemap@sigma-star.at, adobriyan@gmail.com, wangkefeng.wang@huawei.com, ryan.roberts@arm.com, hughd@google.com, peterx@redhat.com, avagin@google.com, lstoakes@gmail.com, vbabka@suse.cz, akpm@linux-foundation.org, usama.anjum@collabora.com, corbet@lwn.net References: <20240306232339.29659-1-richard@nod.at> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240306232339.29659-1-richard@nod.at> 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-Queue-Id: E26D64000F X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: oyx8h94wumzo9n9qtzzuh8snh1kbbonz X-HE-Tag: 1709808742-438102 X-HE-Meta: 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 7k5jn9Nd XdHXo+tynkbx7rtQKr3zbWNP18jm9WuQAYlN2thh11if/hmAs/hUZGX667Ol9iiuABSDwXFVr/tYn58B4VuH4T/qUNJhGP/PUnEq1LhV02hFDmXCIs9L0kflufibsYeIcnZ2v5BhxwaRG9Hzf8sII9Leg2G91xb8bQJeSDYFyWZagkm2aeMAAKgbGtj/c7/0fYJ2NaIOS60cpvZH39AGxMU2QnSkREe0MZqX/DPNRBoTn6E2QZIEJ1znXow== 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: List-Subscribe: List-Unsubscribe: On 07.03.24 00:23, Richard Weinberger wrote: > Is a PTE present and writable, bit 58 will be set. > This allows detecting CoW memory mappings and other mappings > where a write access will cause a page fault. > But why is that required? What is the target use case? (I did not get the cover letter in my inbox) We're running slowly but steadily out of bits, so we better make wise decisions. Also, consider: Architectures where the dirty/access bit is not HW managed could indicate "writable" here although we *will* get a page fault to set the page dirty/accessed. So best this can universally do is say "this PTE currently has write permissions". > Signed-off-by: Richard Weinberger > --- > fs/proc/task_mmu.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 3f78ebbb795f..7c7e0e954c02 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1341,6 +1341,7 @@ struct pagemapread { > #define PM_SOFT_DIRTY BIT_ULL(55) > #define PM_MMAP_EXCLUSIVE BIT_ULL(56) > #define PM_UFFD_WP BIT_ULL(57) > +#define PM_WRITE BIT_ULL(58) > #define PM_FILE BIT_ULL(61) > #define PM_SWAP BIT_ULL(62) > #define PM_PRESENT BIT_ULL(63) > @@ -1417,6 +1418,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm, > flags |= PM_SOFT_DIRTY; > if (pte_uffd_wp(pte)) > flags |= PM_UFFD_WP; > + if (pte_write(pte)) > + flags |= PM_WRITE; > } else if (is_swap_pte(pte)) { > swp_entry_t entry; > if (pte_swp_soft_dirty(pte)) > @@ -1483,6 +1486,8 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, > flags |= PM_SOFT_DIRTY; > if (pmd_uffd_wp(pmd)) > flags |= PM_UFFD_WP; > + if (pmd_write(pmd)) > + flags |= PM_WRITE; > if (pm->show_pfn) > frame = pmd_pfn(pmd) + > ((addr & ~PMD_MASK) >> PAGE_SHIFT); > @@ -1586,6 +1591,9 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask, > if (huge_pte_uffd_wp(pte)) > flags |= PM_UFFD_WP; > > + if (pte_write(pte)) > + flags |= PM_WRITE; > + > flags |= PM_PRESENT; > if (pm->show_pfn) > frame = pte_pfn(pte) + -- Cheers, David / dhildenb