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[211.76.176.103]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82f0c30ee4bsm15916663b3a.2.2026.04.14.08.14.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Apr 2026 08:14:52 -0700 (PDT) Message-ID: <6125defb-3aa4-494c-abed-982be684f839@gmail.com> Date: Tue, 14 Apr 2026 23:14:39 +0800 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 v3 13/13] mm/huge_memory: add and use has_deposited_pgtable() To: "David Hildenbrand (Arm)" , Lorenzo Stoakes Cc: Andrew Morton , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <41b1ff54-c120-42ae-8b74-54767abf3554@gmail.com> <2f29f66b-46db-4925-b922-4add61b633bf@gmail.com> <53d748d3-4150-4e7b-8c1f-4c58587e9183@kernel.org> Content-Language: en-US From: Yin Tirui In-Reply-To: <53d748d3-4150-4e7b-8c1f-4c58587e9183@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/14/26 17:44, David Hildenbrand (Arm) wrote: > > I mean, we need some indication to know also during folio splitting > whether we can just discard the PMD, as we can refault it later, or > whether we really have to install a PTE table. > > What if someone used remap_pfn_range() on some part of the VMA, and > faults on another part? > > Doesn't really work. > > Do we have users of remap_pfn_range() that have ->fault set? If not, we > should probably just disallow this combination. I did a quick tree-wide grep: $ git grep -l "remap_pfn_range" | xargs grep -l "\.fault\s*=" arch/powerpc/platforms/book3s/vas-api.c drivers/infiniband/hw/hfi1/file_ops.c drivers/uio/uio.c drivers/vfio/pci/vfio_pci_core.c fs/proc/vmcore.c security/selinux/selinuxfs.c It turns out there are two users of this "hybrid" approach in the kernel: 1. fs/proc/vmcore.c: It pre-maps via remap_pfn_range() but registers mmap_vmcore_fault(). 2. arch/powerpc/platforms/book3s/vas-api.c: It pre-maps via remap_pfn_range(), but registers vas_mmap_fault(). > > Then we know for sure whether something was installed through > remap_pfn_range() or through a fault handler. > How would you suggest we proceed here? -- Yin Tirui