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[2003:d8:2f34:a300:1c2c:f35e:e8e5:488e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7fc1b60sm117663315e9.34.2025.06.02.02.33.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Jun 2025 02:33:09 -0700 (PDT) Message-ID: <9c465b24-8775-4852-9618-0873cbf2aaf7@redhat.com> Date: Mon, 2 Jun 2025 11:33:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 07/12] mm: Remove redundant pXd_devmap calls To: Alistair Popple , linux-mm@kvack.org Cc: 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 References: <2ee5a64581d2c78445e5c4180d7eceed085825ca.1748500293.git-series.apopple@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250602_023315_712331_DD135B60 X-CRM114-Status: GOOD ( 11.48 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1398,10 +1398,7 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > } > > entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); > - if (pfn_t_devmap(pfn)) > - entry = pmd_mkdevmap(entry); > - else > - entry = pmd_mkspecial(entry); > + entry = pmd_mkspecial(entry); > if (write) { I just stumbled over this, and I think there is something off here in the PMD/PUD case. vmf_insert_folio_pmd() does a folio_get() + folio_add_file_rmap_pmd(). But then, we go ahead and turn this into a special mapping by setting it pmd_mkdevmap()/pmd_mkspecial(). Consequently, vm_normal_page_pmd() would ignore them, not following the rules documented for vm_normal_page() and behaving differently than vmf_insert_page_mkwrite()->insert_page(). folio_add_file_rmap_pmd() should never set these things special/devmap in the first place :/ What am I missing? Note that fs/dax.c calls vmf_insert_folio_pmd() for PMDs and vmf_insert_page_mkwrite() for PTEs. Consequently, PTEs will never be marked special (corner case, shared zeropage), but PMDs would always. Hm? -- Cheers, David / dhildenb