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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 43/47] mm/huge_memory: split huge PUDs when adjusting VMA boundaries Message-ID: References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> <20261029-fixes_core-v2-43-a64ce7f83abb@kernel.org> X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261029-fixes_core-v2-43-a64ce7f83abb@kernel.org> On Thu, Oct 29, 2026 at 09:33:38PM +0100, David Hildenbrand (Arm) wrote: > PFN mappings such as VFIO PCI BAR mappings can use PUD leaves while > allowing VMA splits at page granularity. However, vma_adjust_trans_huge() > only handles PMDs. > > After faulting a writable PUD-sized VFIO BAR mapping, changing its first > page to read-only with mprotect() makes the PMD walk treat the PUD leaf > as a PMD table. Applying MADV_DONTFORK to the first PMD-sized chunk leaves > the PUD spanning two VMAs: the PMD-aligned boundary skips splitting. > > Walk the page tables once at each adjusted boundary and split a huge > PUD or PMD leaf as needed. Handle PUD leaves even when the boundary is > PMD-aligned. > > Fixes: f9e54c3a2f5b7 ("vfio/pci: implement huge_fault support") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov