From: Pratyush Yadav To prepare a shmem inode for live update via the Live Update Orchestrator (LUO), its index -> folio mappings must be serialized. Once the mappings are serialized, they cannot change since it would cause the serialized data to become inconsistent. This can be done by pinning the folios to avoid migration, and by making sure no folios can be added to or removed from the inode. While mechanisms to pin folios already exist, the only way to stop folios being added or removed are the grow and shrink file seals. But file seals come with their own semantics, one of which is that they can't be removed. This doesn't work with liveupdate since it can be cancelled or error out, which would need the seals to be removed and the file's normal functionality to be restored. Introduce SHMEM_F_MAPPING_FROZEN to indicate this instead. It is internal to shmem and is not directly exposed to userspace. It functions similar to F_SEAL_GROW | F_SEAL_SHRINK, but additionally disallows hole punching, and can be removed. Signed-off-by: Pratyush Yadav Signed-off-by: Pasha Tatashin --- include/linux/shmem_fs.h | 17 +++++++++++++++++ mm/shmem.c | 12 +++++++++++- 2 files changed, 28 insertions(+), 1 deletion(-) diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index 923f0da5f6c4..f68fc14f7664 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -24,6 +24,14 @@ struct swap_iocb; #define SHMEM_F_NORESERVE BIT(0) /* Disallow swapping. */ #define SHMEM_F_LOCKED BIT(1) +/* + * Disallow growing, shrinking, or hole punching in the inode. Combined with + * folio pinning, makes sure the inode's mapping stays fixed. + * + * In some ways similar to F_SEAL_GROW | F_SEAL_SHRINK, but can be removed and + * isn't directly visible to userspace. + */ +#define SHMEM_F_MAPPING_FROZEN BIT(2) struct shmem_inode_info { spinlock_t lock; @@ -186,6 +194,15 @@ static inline bool shmem_file(struct file *file) return shmem_mapping(file->f_mapping); } +/* Must be called with inode lock taken exclusive. */ +static inline void shmem_i_mapping_freeze(struct inode *inode, bool freeze) +{ + if (freeze) + SHMEM_I(inode)->flags |= SHMEM_F_MAPPING_FROZEN; + else + SHMEM_I(inode)->flags &= ~SHMEM_F_MAPPING_FROZEN; +} + /* * If fallocate(FALLOC_FL_KEEP_SIZE) has been used, there may be pages * beyond i_size's notion of EOF, which fallocate has committed to reserving: diff --git a/mm/shmem.c b/mm/shmem.c index 8e6b3f003da5..ef57e2649a41 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1329,7 +1329,8 @@ static int shmem_setattr(struct mnt_idmap *idmap, loff_t newsize = attr->ia_size; /* protected by i_rwsem */ - if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) || + if ((info->flags & SHMEM_F_MAPPING_FROZEN) || + (newsize < oldsize && (info->seals & F_SEAL_SHRINK)) || (newsize > oldsize && (info->seals & F_SEAL_GROW))) return -EPERM; @@ -3352,6 +3353,10 @@ shmem_write_begin(const struct kiocb *iocb, struct address_space *mapping, return -EPERM; } + if (unlikely((info->flags & SHMEM_F_MAPPING_FROZEN) && + pos + len > inode->i_size)) + return -EPERM; + ret = shmem_get_folio(inode, index, pos + len, &folio, SGP_WRITE); if (ret) return ret; @@ -3725,6 +3730,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, inode_lock(inode); + if (info->flags & SHMEM_F_MAPPING_FROZEN) { + error = -EPERM; + goto out; + } + if (mode & FALLOC_FL_PUNCH_HOLE) { struct address_space *mapping = file->f_mapping; loff_t unmap_start = round_up(offset, PAGE_SIZE); -- 2.50.1.565.gc32cd1483b-goog