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Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH RFC 13/17] mm: introduce VM_FAULT_UFFD_MISSING fault reason Date: Tue, 27 Jan 2026 21:29:32 +0200 Message-ID: <20260127192936.1250096-14-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260127192936.1250096-1-rppt@kernel.org> References: <20260127192936.1250096-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1457540005 X-Stat-Signature: zdj3ddb8efrwxzxom39g53w38fn88u4y X-Rspam-User: X-HE-Tag: 1769542269-311702 X-HE-Meta: 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 mHoz577y jlxVr5Dn9ea/1tKvfxgqzhhO6A/1dkRDycpkh5qSAZ8qt/Mqvy8Kd1aX07h1LvaiNkuUgt3yd9B0gdUyGp/DZfZ62xTSACUW6j4B20FUDkeCV1IpCYcMiJWlE0gXJtyeIb94HXQfiWkSLUc7KZEprhgjLDoql3wD6xshGVH+dvaTLgeFBilpUdFIEI8k/1Zh/8+sRYUabUL+vHa6Yp+pLUtp7Jsr2rZ7jvwMVPoVvvGmyweYNuFhR88kIaXLg7D4ztv73xKpm0/jP9MkAdAnP2BaWIZ7jbbzfvDUIBJpwqTbCDjqdwGZOXJcSn/fsCTNKcTopx51WUkrPgNX7eUOfOu7qyg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Nikita Kalyazin When a VMA is registered with userfaulfd in missing mode, its ->fault() method should check if a folio exists in the page cache and if no ->fault() should call handle_userfault(VM_UFFD_MISSING). Instead of calling handle_userfault() directly from a specific ->fault() implementation introduce new fault reason VM_FAULT_UFFD_MISSING that will notify the core page fault handler that it should call handle_userfaultfd(VM_UFFD_MISSING) to complete a page fault. Replace a call to handle_userfault(VM_UFFD_MISSING) in shmem and use the new VM_FAULT_UFFD_MISSING there instead. For configurations that don't enable CONFIG_USERFAULTFD, VM_FAULT_UFFD_MISSING is set to 0. Signed-off-by: Nikita Kalyazin Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm_types.h | 7 ++++++- mm/memory.c | 5 ++++- mm/shmem.c | 2 +- 3 files changed, 11 insertions(+), 3 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index b25ac322bfbf..a061c43e835b 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1557,6 +1557,8 @@ typedef __bitwise unsigned int vm_fault_t; * @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock released * @VM_FAULT_UFFD_MINOR: ->fault did not modify page tables and needs * handle_userfault(VM_UFFD_MINOR) to complete + * @VM_FAULT_UFFD_MISSING: ->fault did not modify page tables and needs + * handle_userfault(VM_UFFD_MISSING) to complete * @VM_FAULT_HINDEX_MASK: mask HINDEX value * */ @@ -1576,8 +1578,10 @@ enum vm_fault_reason { VM_FAULT_COMPLETED = (__force vm_fault_t)0x004000, #ifdef CONFIG_USERFAULTFD VM_FAULT_UFFD_MINOR = (__force vm_fault_t)0x008000, + VM_FAULT_UFFD_MISSING = (__force vm_fault_t)0x010000, #else VM_FAULT_UFFD_MINOR = (__force vm_fault_t)0x000000, + VM_FAULT_UFFD_MISSING = (__force vm_fault_t)0x000000, #endif VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000, }; @@ -1604,7 +1608,8 @@ enum vm_fault_reason { { VM_FAULT_DONE_COW, "DONE_COW" }, \ { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }, \ { VM_FAULT_COMPLETED, "COMPLETED" }, \ - { VM_FAULT_UFFD_MINOR, "UFFD_MINOR" } + { VM_FAULT_UFFD_MINOR, "UFFD_MINOR" }, \ + { VM_FAULT_UFFD_MISSING, "UFFD_MISSING" } struct vm_special_mapping { const char *name; /* The name, e.g. "[vdso]". */ diff --git a/mm/memory.c b/mm/memory.c index fcb3e0c3113e..f72e69a43b68 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5319,9 +5319,12 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) ret = vma->vm_ops->fault(vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | - VM_FAULT_DONE_COW | VM_FAULT_UFFD_MINOR))) { + VM_FAULT_DONE_COW | VM_FAULT_UFFD_MINOR | + VM_FAULT_UFFD_MISSING))) { if (ret & VM_FAULT_UFFD_MINOR) return handle_userfault(vmf, VM_UFFD_MINOR); + if (ret & VM_FAULT_UFFD_MISSING) + return handle_userfault(vmf, VM_UFFD_MISSING); return ret; } diff --git a/mm/shmem.c b/mm/shmem.c index 6aa905147c0c..1bc544cab2a8 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2530,7 +2530,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, */ if (vma && userfaultfd_missing(vma)) { - *fault_type = handle_userfault(vmf, VM_UFFD_MISSING); + *fault_type = VM_FAULT_UFFD_MISSING; return 0; } -- 2.51.0