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Thu, 12 Nov 2026 02:09:00 -0800 (PST) Message-ID: <048ba947-e63c-4361-8982-b40372d4f062@gmail.com> Date: Thu, 12 Nov 2026 11:08:58 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] mm/huge_memory: use the large-page PAT encoding for huge pfn mappings To: Eliav Farber , Andrew Morton , David Hildenbrand , Zi Yan Cc: Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , x86@kernel.org, William Kucharski , Vishal Moola , Alex Williamson , Matthew Wilcox , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261112051440.16140-1-farbere@amazon.com> <20261112051440.16140-5-farbere@amazon.com> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261112051440.16140-5-farbere@amazon.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: s8hxddy3o91rfcq77i19dfomdkrr57jw X-Rspamd-Queue-Id: 150F4140005 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-9.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794478142-863163 X-HE-Meta: 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 PaI7jZSQ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/12/26 6:14 AM, Eliav Farber wrote: > insert_pmd() and insert_pud() build the entry from the pgprot that > vmf_insert_pfn_pmd()/_pud() took from vma->vm_page_prot and passed > through pfnmap_setup_cachemode_pfn(). That pgprot carries the PTE-level > cache mode encoding, but x86 keeps the high PAT bit at bit 7 for a PTE > (_PAGE_BIT_PAT) and at bit 12 for a PMD or PUD (_PAGE_BIT_PAT_LARGE), > where bit 7 is _PAGE_PSE. > > A memtype that needs that bit, write-through or write-protect, loses it: > the cache mode index of the huge entry drops from 4-7 to 0-3. With the > PAT slots Linux programs, write-through (slot 7) becomes UC (slot 3), > and write-protect (slot 5) becomes write-combining (slot 1), which loses > the write protection. The other x86 paths that build a large entry from > a PTE pgprot convert it first, see populate_pmd() and populate_pud(). > > Convert in the two huge pfn paths. Add a generic pgprot_4k_2_large() > that returns its argument unchanged, so that only architectures which > encode the levels differently have to define it, and x86's existing > definition is picked up. > > The folio paths keep using vma->vm_page_prot as is. They map > struct-page-backed memory, which x86 maps write-back. > > Fixes: 5cad465d7fa6 ("mm: add vmf_insert_pfn_pmd()") > Signed-off-by: Eliav Farber LGTM: Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a