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(p200300d82f199c0005687df700e1293d.dip0.t-ipconnect.de. [2003:d8:2f19:9c00:568:7df7:e1:293d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a5323ab1a2sm1165901f8f.28.2025.06.06.01.23.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 01:23:14 -0700 (PDT) Message-ID: Date: Fri, 6 Jun 2025 10:23:11 +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 v1 1/2] mm/huge_memory: don't mark refcounted pages special in vmf_insert_folio_pmd() To: Oscar Salvador Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, Andrew Morton , Alistair Popple , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Dan Williams References: <20250603211634.2925015-1-david@redhat.com> <20250603211634.2925015-2-david@redhat.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06.06.25 10:20, Oscar Salvador wrote: > On Tue, Jun 03, 2025 at 11:16:33PM +0200, David Hildenbrand wrote: >> Marking PMDs that map a "normal" refcounted folios as special is >> against our rules documented for vm_normal_page(). >> >> Fortunately, there are not that many pmd_special() check that can be >> mislead, and most vm_normal_page_pmd()/vm_normal_folio_pmd() users that >> would get this wrong right now are rather harmless: e.g., none so far >> bases decisions whether to grab a folio reference on that decision. >> >> Well, and GUP-fast will fallback to GUP-slow. All in all, so far no big >> implications as it seems. >> >> Getting this right will get more important as we use >> folio_normal_page_pmd() in more places. >> >> Fix it by just inlining the relevant code, making the whole >> pmd_none() handling cleaner. We can now use folio_mk_pmd(). >> >> While at it, make sure that a pmd that is not-none is actually present >> before comparing PFNs. >> >> Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()") >> Signed-off-by: David Hildenbrand > > Hi David, > >> --- >> mm/huge_memory.c | 39 ++++++++++++++++++++++++++++++++------- >> 1 file changed, 32 insertions(+), 7 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index d3e66136e41a3..f9e23dfea76f8 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -1474,9 +1474,10 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, >> struct vm_area_struct *vma = vmf->vma; >> unsigned long addr = vmf->address & PMD_MASK; >> struct mm_struct *mm = vma->vm_mm; >> + pmd_t *pmd = vmf->pmd; >> spinlock_t *ptl; >> pgtable_t pgtable = NULL; >> - int error; >> + pmd_t entry; >> >> if (addr < vma->vm_start || addr >= vma->vm_end) >> return VM_FAULT_SIGBUS; >> @@ -1490,17 +1491,41 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, >> return VM_FAULT_OOM; >> } >> >> - ptl = pmd_lock(mm, vmf->pmd); >> - if (pmd_none(*vmf->pmd)) { >> + ptl = pmd_lock(mm, pmd); >> + if (pmd_none(*pmd)) { >> folio_get(folio); >> folio_add_file_rmap_pmd(folio, &folio->page, vma); >> add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR); >> + >> + entry = folio_mk_pmd(folio, vma->vm_page_prot); >> + if (write) { >> + entry = pmd_mkyoung(pmd_mkdirty(entry)); >> + entry = maybe_pmd_mkwrite(entry, vma); >> + } >> + set_pmd_at(mm, addr, pmd, entry); >> + update_mmu_cache_pmd(vma, addr, pmd); >> + >> + if (pgtable) { >> + pgtable_trans_huge_deposit(mm, pmd, pgtable); >> + mm_inc_nr_ptes(mm); >> + pgtable = NULL; >> + } >> + } else if (pmd_present(*pmd) && write) { >> + /* >> + * We only allow for upgrading write permissions if the >> + * same folio is already mapped. >> + */ >> + if (pmd_pfn(*pmd) == folio_pfn(folio)) { >> + entry = pmd_mkyoung(*pmd); >> + entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); >> + if (pmdp_set_access_flags(vma, addr, pmd, entry, 1)) >> + update_mmu_cache_pmd(vma, addr, pmd); >> + } else { >> + WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); >> + } > > So, this is pretty much insert_pfn_pmd without pmd_mkdevmap/pmd_mkspecial(). > I guess vmf_inser_folio_pmd() doesn't have to be concerned with devmaps > either, right? > > Looks good to me, just a nit: would it not be better to pass a boolean > to insert_pfn_pmd() that lets it know whether it "can" create a > devmap/special entries? See my reply to Dan. Yet another boolean, yuck. Passing the folio and the pfn, yuck. (I have a strong opinion here ;) ) -- Cheers, David / dhildenb