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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532e13d014sm171119765e9.24.2025.06.17.02.49.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 02:49:05 -0700 (PDT) Message-ID: <1709a271-273b-4668-b813-648e5785e4e8@redhat.com> Date: Tue, 17 Jun 2025 11:49:03 +0200 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/14] mm: Convert vmf_insert_mixed() from using pte_devmap to pte_special 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, Jason Gunthorpe References: <5c03174d2ea76f579e4675f5fab6277f5dd91be2.1750075065.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: <5c03174d2ea76f579e4675f5fab6277f5dd91be2.1750075065.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: > DAX no longer requires device PTEs as it always has a ZONE_DEVICE page > associated with the PTE that can be reference counted normally. Other users > of pte_devmap are drivers that set PFN_DEV when calling vmf_insert_mixed() > which ensures vm_normal_page() returns NULL for these entries. > > There is no reason to distinguish these pte_devmap users so in order to > free up a PTE bit use pte_special instead for entries created with > vmf_insert_mixed(). This will ensure vm_normal_page() will continue to > return NULL for these pages. > > Architectures that don't support pte_special also don't support pte_devmap > so those will continue to rely on pfn_valid() to determine if the page can > be mapped. > > Signed-off-by: Alistair Popple > Reviewed-by: Jason Gunthorpe > Reviewed-by: Dan Williams > --- > mm/hmm.c | 3 --- > mm/memory.c | 20 ++------------------ > mm/vmscan.c | 2 +- > 3 files changed, 3 insertions(+), 22 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 5311753..1a3489f 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -302,13 +302,10 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, > goto fault; > > /* > - * Bypass devmap pte such as DAX page when all pfn requested > - * flags(pfn_req_flags) are fulfilled. > * Since each architecture defines a struct page for the zero page, just > * fall through and treat it like a normal page. > */ > if (!vm_normal_page(walk->vma, addr, pte) && > - !pte_devmap(pte) && > !is_zero_pfn(pte_pfn(pte))) { > if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) { > pte_unmap(ptep); > diff --git a/mm/memory.c b/mm/memory.c > index b0cda5a..2c6eda1 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -598,16 +598,6 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > return NULL; > if (is_zero_pfn(pfn)) > return NULL; > - if (pte_devmap(pte)) > - /* > - * NOTE: New users of ZONE_DEVICE will not set pte_devmap() > - * and will have refcounts incremented on their struct pages > - * when they are inserted into PTEs, thus they are safe to > - * return here. Legacy ZONE_DEVICE pages that set pte_devmap() > - * do not have refcounts. Example of legacy ZONE_DEVICE is > - * MEMORY_DEVICE_FS_DAX type in pmem or virtio_fs drivers. > - */ > - return NULL; > > print_bad_pte(vma, addr, pte, NULL); > return NULL; > @@ -2483,10 +2473,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr, > } > > /* Ok, finally just insert the thing.. */ > - if (pfn_t_devmap(pfn)) > - entry = pte_mkdevmap(pfn_t_pte(pfn, prot)); > - else > - entry = pte_mkspecial(pfn_t_pte(pfn, prot)); > + entry = pte_mkspecial(pfn_t_pte(pfn, prot)); > > if (mkwrite) { > entry = pte_mkyoung(entry); > @@ -2597,8 +2584,6 @@ static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn, bool mkwrite) > /* these checks mirror the abort conditions in vm_normal_page */ > if (vma->vm_flags & VM_MIXEDMAP) > return true; > - if (pfn_t_devmap(pfn)) > - return true; > if (pfn_t_special(pfn)) > return true; > if (is_zero_pfn(pfn_t_to_pfn(pfn))) > @@ -2630,8 +2615,7 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma, > * than insert_pfn). If a zero_pfn were inserted into a VM_MIXEDMAP > * without pte special, it would there be refcounted as a normal page. > */ > - if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && > - !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) { > + if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pfn_t_valid(pfn)) { > struct page *page; > > /* > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a93a1ba..85bf782 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3424,7 +3424,7 @@ static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned > if (!pte_present(pte) || is_zero_pfn(pfn)) > return -1; > > - if (WARN_ON_ONCE(pte_devmap(pte) || pte_special(pte))) > + if (WARN_ON_ONCE(pte_special(pte))) > return -1; > > if (!pte_young(pte) && !mm_has_notifiers(vma->vm_mm)) -- Cheers, David / dhildenb