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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 1/3] drivers/char/mem: eliminate unnecessary use of success_hook Date: Tue, 2 Jun 2026 12:06:25 +0100 Message-ID: <010579cca6787cf7bb057ab1f7228978b10601c8.1780397980.git.ljs@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: BE0FD40015 X-Stat-Signature: sk7ezaci64o7hphz1c5yc59apti591hi X-Rspam-User: X-HE-Tag: 1780398399-188157 X-HE-Meta: U2FsdGVkX18C8IxODKkEHbvBF0OuaAdztTpxcl0PZfnc099bfY/Pmyc3YFUEwB8VYPSLY9M4+5HqDxMbeSfuM2HToh1LI1J1542j394ENhriy6JiPohvdv34mOHHiTkpH3YK0t8vcfBzoj4aNDCNDrd8dg8vnjcaH0pm/n2x+JN5zSp06yZPbBdnNoQ09sdH/QuosSMYQxZQ/j2K67PbiM5PfksHfkxGicXjwti6qQPx0nnR6XUgOS5yqEotoeN45XBq/Zf+KxG7IKtYRDmSG6IEHfPy0au/IZZgnj4r8THnzrsfPkeAP8t7W1hm43PjUGgKM4GrVssTv/iYEqQ9+DBySS+Cv9bayoBDS4A+SWy/U8mdKVIhTFa3HEvFgMznrVLpEijcF75PsCSqJLHzs56mKfLXYlozd1iWBTxnjis8D7c4HpFeif1VROXZ0b0Q+4lmITg+HSzt/IvmMDm8xtwCfmxmTeIcHqb56I+/C93lKAZGgs/eSXwUIDQ8d3x8000P30XISLRVosiyeFUmKH4K19woVdH1rlSaKYOWRqdn5yVKS6qVOGbZwS0vYr39P0sUAMKERSMEZMr7mJ3kOJxNl3EkRFFyjbl01Cs4H4Y0G0PL3rzkOZoeEywE26NFYLkUDmF03D9YewL7MN+g7yxJPxNmk1TW/yXgQIHkSfalg86L08TilSdg8PZXhWg8Fre7qUtMwZHZBLmaYfg7BPpiBa+DSiEod2OBiAiyag9DupBCUUHEGhTEGM4DPc0S02fJQumqOnazTozm/bYPVcV4cNpdprHBgGvQ+jwBeLANczCJshUNQ+pkTj6x/+2yuRKuRY+Q3ssBGg9UdBjTTWVn6iddQDricXsQ8WPkoENI5uDCZGWJIsokNjI8eXjY2HCkN0zG8HahxW6xZrc67D5WiETdsYapzA6Z5+aXXTFKlQNXcxA7hVtNvwSdPrVo6mS5pdRPalJqbKC2Pcu XJQf/tMn sG1Bl+UkCfozMKdJ3L4VJNzWWbXQ2zA77Ydt1CpuRru8FS/4+g6C1OzoHuqRgMYX6CDwSXcbgYV3mV9nvMRlPq/1JpsCRhl3150Lx8StgfxOVELsmAzZqmmiE/0TC/xcMNxeeVbL02Z34krGijMtK9cmCZp7dZ5x3TR3484jUrJlLMDr15DU1bm94Mn3u1nZ9DXpCkoeaERrCK07cl+aMd8S3GicOKywU57VP44vP8hGZOMv2+1Bzl09WIZcBR6yeMEsbUbV2ZCP3imTn+cr+w68s0A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: /dev/zero, uniquely, marks memory mapped there as anonymous. This is currently achieved using the mmap_action->success_hook. However this hook circumvents the abstraction of VMA initialisation so it's preferable to do things a different way. To achieve this, this patch firstly defaults the VMA descriptor's vm_ops field to the dummy VMA operations, which is what file-backed VMAs default this field to. That way, we can detect whether a driver sets this field to NULL in order to mark it anonymous. We then introduce vma_desc_set_anonymous() to do this explicitly, and invoke it in mmap_zero_prepare(). This way, any driver which does not explicitly set desc->vm_ops, retains the dummy vm_ops as they would previously. We also update set_vma_user_defined_fields() to make clear that we are either setting vma->vm_ops to what is provided by the driver (or defaulting to dummy_vm_ops if not set), or setting the VMA anonymous. This lays the groundwork for removing the success hook. Signed-off-by: Lorenzo Stoakes Acked-by: David Hildenbrand (Arm) --- drivers/char/mem.c | 17 +++++------------ include/linux/mm.h | 5 +++++ mm/util.c | 1 + mm/vma.c | 3 +++ tools/testing/vma/include/dup.h | 1 + 5 files changed, 15 insertions(+), 12 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 5fd421e48c04..a4297eb39887 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -504,17 +504,6 @@ static ssize_t read_zero(struct file *file, char __user *buf, return cleared; } -static int mmap_zero_private_success(const struct vm_area_struct *vma) -{ - /* - * This is a highly unique situation where we mark a MAP_PRIVATE mapping - * of /dev/zero anonymous, despite it not being. - */ - vma_set_anonymous((struct vm_area_struct *)vma); - - return 0; -} - static int mmap_zero_prepare(struct vm_area_desc *desc) { #ifndef CONFIG_MMU @@ -523,7 +512,11 @@ static int mmap_zero_prepare(struct vm_area_desc *desc) if (vma_desc_test(desc, VMA_SHARED_BIT)) return shmem_zero_setup_desc(desc); - desc->action.success_hook = mmap_zero_private_success; + /* + * This is a highly unique situation where we mark a MAP_PRIVATE mapping + * of /dev/zero anonymous, despite it not being. + */ + vma_desc_set_anonymous(desc); return 0; } diff --git a/include/linux/mm.h b/include/linux/mm.h index 11f440e9d7cd..0f2612a70fb1 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1489,6 +1489,11 @@ static inline void vma_set_anonymous(struct vm_area_struct *vma) vma->vm_ops = NULL; } +static inline void vma_desc_set_anonymous(struct vm_area_desc *desc) +{ + desc->vm_ops = NULL; +} + static inline bool vma_is_anonymous(struct vm_area_struct *vma) { return !vma->vm_ops; diff --git a/mm/util.c b/mm/util.c index 3cc949a0b7ed..2b2a9df689d7 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1192,6 +1192,7 @@ void compat_set_desc_from_vma(struct vm_area_desc *desc, desc->vm_file = vma->vm_file; desc->vma_flags = vma->flags; desc->page_prot = vma->vm_page_prot; + desc->vm_ops = vma->vm_ops; /* Default. */ desc->action.type = MMAP_NOTHING; diff --git a/mm/vma.c b/mm/vma.c index d90791b00a7b..9eea2850818a 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2697,6 +2697,8 @@ static void set_vma_user_defined_fields(struct vm_area_struct *vma, { if (map->vm_ops) vma->vm_ops = map->vm_ops; + else /* Only /dev/zero should do this. */ + vma_set_anonymous(vma); vma->vm_private_data = map->vm_private_data; } @@ -2744,6 +2746,7 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr, .action = { .type = MMAP_NOTHING, /* Default to no further action. */ }, + .vm_ops = &vma_dummy_vm_ops, }; bool allocated_new = false; int error; diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 9e0dfd3a85b0..306171d061e7 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -1303,6 +1303,7 @@ static inline void compat_set_desc_from_vma(struct vm_area_desc *desc, desc->vm_file = vma->vm_file; desc->vma_flags = vma->flags; desc->page_prot = vma->vm_page_prot; + desc->vm_ops = vma->vm_ops; /* Default. */ desc->action.type = MMAP_NOTHING; -- 2.54.0