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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b087f8sm13629833f8f.53.2025.06.17.02.25.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 02:25:15 -0700 (PDT) Message-ID: <6afc2e67-3ecb-41a5-9c8f-00ecd64f035a@redhat.com> Date: Tue, 17 Jun 2025 11:25:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 02/14] mm: Filter zone device pages returned from folio_walk_start() To: Alistair Popple , akpm@linux-foundation.org Cc: linux-mm@kvack.org, gerald.schaefer@linux.ibm.com, dan.j.williams@intel.com, jgg@ziepe.ca, willy@infradead.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, zhang.lyra@gmail.com, debug@rivosinc.com, bjorn@kernel.org, balbirs@nvidia.com, lorenzo.stoakes@oracle.com, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-cxl@vger.kernel.org, dri-devel@lists.freedesktop.org, John@Groves.net, m.szyprowski@samsung.com References: <11dd5b70546ec67593a4bf79f087b113f15d6bb1.1750075065.git-series.apopple@nvidia.com> From: David Hildenbrand Content-Language: en-US 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: <11dd5b70546ec67593a4bf79f087b113f15d6bb1.1750075065.git-series.apopple@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.06.25 13:58, Alistair Popple wrote: > Previously dax pages were skipped by the pagewalk code as pud_special() or > vm_normal_page{_pmd}() would be false for DAX pages. Now that dax pages are > refcounted normally that is no longer the case, so the pagewalk code will > start returning them. > > Most callers already explicitly filter for DAX or zone device pages so > don't need updating. However some don't, so add checks to those callers. > > Signed-off-by: Alistair Popple > > --- > > Changes since v1: > > - Dropped "mm/pagewalk: Skip dax pages in pagewalk" and replaced it > with this new patch for v2 > > - As suggested by David and Jason we can filter the folios in the > callers instead of doing it in folio_start_walk(). Most callers > already do this (see below). > > I audited all callers of folio_walk_start() and found the following: > > mm/ksm.c: > > break_ksm() - doesn't need to filter zone_device pages because the can > never be KSM pages. > > get_mergeable_page() - already filters out zone_device pages. > scan_get_next_rmap_iterm() - already filters out zone_device_pages. > > mm/huge_memory.c: > > split_huge_pages_pid() - already checks for DAX with > vma_not_suitable_for_thp_split() > > mm/rmap.c: > > make_device_exclusive() - only works on anonymous pages, although > there'd be no issue with finding a DAX page even if support was extended > to file-backed pages. > > mm/migrate.c: > > add_folio_for_migration() - already checks the vma with vma_migratable() > do_pages_stat_array() - explicitly checks for zone_device folios > > kernel/event/uprobes.c: > > uprobe_write_opcode() - only works on anonymous pages, not sure if > zone_device could ever work so add an explicit check > > arch/s390/mm/fault.c: > > do_secure_storage_access() - not sure so be conservative and add a check > > arch/s390/kernel/uv.c: > > make_hva_secure() - not sure so be conservative and add a check > --- > arch/s390/kernel/uv.c | 2 +- > arch/s390/mm/fault.c | 2 +- > kernel/events/uprobes.c | 2 +- > 3 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c > index b99478e..55aa280 100644 > --- a/arch/s390/kernel/uv.c > +++ b/arch/s390/kernel/uv.c > @@ -424,7 +424,7 @@ int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header > return -EFAULT; > } > folio = folio_walk_start(&fw, vma, hva, 0); > - if (!folio) { > + if (!folio || folio_is_zone_device(folio)) { > mmap_read_unlock(mm); > return -ENXIO; > } > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c > index e1ad05b..df1a067 100644 > --- a/arch/s390/mm/fault.c > +++ b/arch/s390/mm/fault.c > @@ -449,7 +449,7 @@ void do_secure_storage_access(struct pt_regs *regs) > if (!vma) > return handle_fault_error(regs, SEGV_MAPERR); > folio = folio_walk_start(&fw, vma, addr, 0); > - if (!folio) { > + if (!folio || folio_is_zone_device(folio)) { > mmap_read_unlock(mm); > return; > } Curious, does s390 even support ZONE_DEVICE and could trigger this? > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 8a601df..f774367 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -539,7 +539,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, > } > > ret = 0; > - if (unlikely(!folio_test_anon(folio))) { > + if (unlikely(!folio_test_anon(folio) || folio_is_zone_device(folio))) { > VM_WARN_ON_ONCE(is_register); > folio_put(folio); > goto out; I wonder if __uprobe_write_opcode() would just work with anon device folios? We only modify page content, and conditionally zap the page. Would there be a problem with anon device folios? -- Cheers, David / dhildenb