From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Subject: userfaultfd: non-cooperative: Add fork() event When the mm with uffd-ed vmas fork()-s the respective vmas notify their uffds with the event which contains a descriptor with new uffd. This new descriptor can then be used to get events from the child and populate its mm with data. Note, that there can be different uffd-s controlling different vmas within one mm, so first we should collect all those uffds (and ctx-s) in a list and then notify them all one by one but only once per fork(). The context is created at fork() time but the descriptor, file struct and anon inode object is created at event read time. So some trickery is added to the userfaultfd_ctx_read() to handle the ctx queues' locking vs file creation. Another thing worth noticing is that the task that fork()-s waits for the uffd event to get processed WITHOUT the mmap sem. [aarcange@xxxxxxxxxx: build warning fix] Link: http://lkml.kernel.org/r/20161216144821.5183-10-aarcange@xxxxxxxxxx Link: http://lkml.kernel.org/r/20161216144821.5183-9-aarcange@xxxxxxxxxx Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx> Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> Cc: Michael Rapoport <RAPOPORT@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/userfaultfd.c | 148 ++++++++++++++++++++++++++++- include/linux/userfaultfd_k.h | 13 ++ include/uapi/linux/userfaultfd.h | 15 -- kernel/fork.c | 10 + 4 files changed, 170 insertions(+), 16 deletions(-) diff -puN fs/userfaultfd.c~userfaultfd-non-cooperative-add-fork-event fs/userfaultfd.c --- a/fs/userfaultfd.c~userfaultfd-non-cooperative-add-fork-event +++ a/fs/userfaultfd.c @@ -64,6 +64,12 @@ struct userfaultfd_ctx { struct mm_struct *mm; }; +struct userfaultfd_fork_ctx { + struct userfaultfd_ctx *orig; + struct userfaultfd_ctx *new; + struct list_head list; +}; + struct userfaultfd_wait_queue { struct uffd_msg msg; wait_queue_t wq; @@ -465,9 +471,8 @@ out: return ret; } -static int __maybe_unused userfaultfd_event_wait_completion( - struct userfaultfd_ctx *ctx, - struct userfaultfd_wait_queue *ewq) +static int userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, + struct userfaultfd_wait_queue *ewq) { int ret = 0; @@ -518,6 +523,79 @@ static void userfaultfd_event_complete(s __remove_wait_queue(&ctx->event_wqh, &ewq->wq); } +int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs) +{ + struct userfaultfd_ctx *ctx = NULL, *octx; + struct userfaultfd_fork_ctx *fctx; + + octx = vma->vm_userfaultfd_ctx.ctx; + if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) { + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING); + return 0; + } + + list_for_each_entry(fctx, fcs, list) + if (fctx->orig == octx) { + ctx = fctx->new; + break; + } + + if (!ctx) { + fctx = kmalloc(sizeof(*fctx), GFP_KERNEL); + if (!fctx) + return -ENOMEM; + + ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); + if (!ctx) { + kfree(fctx); + return -ENOMEM; + } + + atomic_set(&ctx->refcount, 1); + ctx->flags = octx->flags; + ctx->state = UFFD_STATE_RUNNING; + ctx->features = octx->features; + ctx->released = false; + ctx->mm = vma->vm_mm; + atomic_inc(&ctx->mm->mm_users); + + userfaultfd_ctx_get(octx); + fctx->orig = octx; + fctx->new = ctx; + list_add_tail(&fctx->list, fcs); + } + + vma->vm_userfaultfd_ctx.ctx = ctx; + return 0; +} + +static int dup_fctx(struct userfaultfd_fork_ctx *fctx) +{ + struct userfaultfd_ctx *ctx = fctx->orig; + struct userfaultfd_wait_queue ewq; + + msg_init(&ewq.msg); + + ewq.msg.event = UFFD_EVENT_FORK; + ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new; + + return userfaultfd_event_wait_completion(ctx, &ewq); +} + +void dup_userfaultfd_complete(struct list_head *fcs) +{ + int ret = 0; + struct userfaultfd_fork_ctx *fctx, *n; + + list_for_each_entry_safe(fctx, n, fcs, list) { + if (!ret) + ret = dup_fctx(fctx); + list_del(&fctx->list); + kfree(fctx); + } +} + static int userfaultfd_release(struct inode *inode, struct file *file) { struct userfaultfd_ctx *ctx = file->private_data; @@ -653,12 +731,49 @@ static unsigned int userfaultfd_poll(str } } +static const struct file_operations userfaultfd_fops; + +static int resolve_userfault_fork(struct userfaultfd_ctx *ctx, + struct userfaultfd_ctx *new, + struct uffd_msg *msg) +{ + int fd; + struct file *file; + unsigned int flags = new->flags & UFFD_SHARED_FCNTL_FLAGS; + + fd = get_unused_fd_flags(flags); + if (fd < 0) + return fd; + + file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, new, + O_RDWR | flags); + if (IS_ERR(file)) { + put_unused_fd(fd); + return PTR_ERR(file); + } + + fd_install(fd, file); + msg->arg.reserved.reserved1 = 0; + msg->arg.fork.ufd = fd; + + return 0; +} + static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, struct uffd_msg *msg) { ssize_t ret; DECLARE_WAITQUEUE(wait, current); struct userfaultfd_wait_queue *uwq; + /* + * Handling fork event requires sleeping operations, so + * we drop the event_wqh lock, then do these ops, then + * lock it back and wake up the waiter. While the lock is + * dropped the ewq may go away so we keep track of it + * carefully. + */ + LIST_HEAD(fork_event); + struct userfaultfd_ctx *fork_nctx = NULL; /* always take the fd_wqh lock before the fault_pending_wqh lock */ spin_lock(&ctx->fd_wqh.lock); @@ -716,6 +831,16 @@ static ssize_t userfaultfd_ctx_read(stru if (uwq) { *msg = uwq->msg; + if (uwq->msg.event == UFFD_EVENT_FORK) { + fork_nctx = (struct userfaultfd_ctx *) + (unsigned long) + uwq->msg.arg.reserved.reserved1; + list_move(&uwq->wq.task_list, &fork_event); + spin_unlock(&ctx->event_wqh.lock); + ret = 0; + break; + } + userfaultfd_event_complete(ctx, uwq); spin_unlock(&ctx->event_wqh.lock); ret = 0; @@ -739,6 +864,23 @@ static ssize_t userfaultfd_ctx_read(stru __set_current_state(TASK_RUNNING); spin_unlock(&ctx->fd_wqh.lock); + if (!ret && msg->event == UFFD_EVENT_FORK) { + ret = resolve_userfault_fork(ctx, fork_nctx, msg); + + if (!ret) { + spin_lock(&ctx->event_wqh.lock); + if (!list_empty(&fork_event)) { + uwq = list_first_entry(&fork_event, + typeof(*uwq), + wq.task_list); + list_del(&uwq->wq.task_list); + __add_wait_queue(&ctx->event_wqh, &uwq->wq); + userfaultfd_event_complete(ctx, uwq); + } + spin_unlock(&ctx->event_wqh.lock); + } + } + return ret; } diff -puN include/linux/userfaultfd_k.h~userfaultfd-non-cooperative-add-fork-event include/linux/userfaultfd_k.h --- a/include/linux/userfaultfd_k.h~userfaultfd-non-cooperative-add-fork-event +++ a/include/linux/userfaultfd_k.h @@ -52,6 +52,9 @@ static inline bool userfaultfd_armed(str return vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP); } +extern int dup_userfaultfd(struct vm_area_struct *, struct list_head *); +extern void dup_userfaultfd_complete(struct list_head *); + #else /* CONFIG_USERFAULTFD */ /* mm helpers */ @@ -76,6 +79,16 @@ static inline bool userfaultfd_armed(str return false; } +static inline int dup_userfaultfd(struct vm_area_struct *vma, + struct list_head *l) +{ + return 0; +} + +static inline void dup_userfaultfd_complete(struct list_head *l) +{ +} + #endif /* CONFIG_USERFAULTFD */ #endif /* _LINUX_USERFAULTFD_K_H */ diff -puN include/uapi/linux/userfaultfd.h~userfaultfd-non-cooperative-add-fork-event include/uapi/linux/userfaultfd.h --- a/include/uapi/linux/userfaultfd.h~userfaultfd-non-cooperative-add-fork-event +++ a/include/uapi/linux/userfaultfd.h @@ -18,12 +18,7 @@ * means the userland is reading). */ #define UFFD_API ((__u64)0xAA) -/* - * After implementing the respective features it will become: - * #define UFFD_API_FEATURES (UFFD_FEATURE_PAGEFAULT_FLAG_WP | \ - * UFFD_FEATURE_EVENT_FORK) - */ -#define UFFD_API_FEATURES (0) +#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK) #define UFFD_API_IOCTLS \ ((__u64)1 << _UFFDIO_REGISTER | \ (__u64)1 << _UFFDIO_UNREGISTER | \ @@ -78,6 +73,10 @@ struct uffd_msg { } pagefault; struct { + __u32 ufd; + } fork; + + struct { /* unused reserved fields */ __u64 reserved1; __u64 reserved2; @@ -90,9 +89,7 @@ struct uffd_msg { * Start at 0x12 and not at 0 to be more strict against bugs. */ #define UFFD_EVENT_PAGEFAULT 0x12 -#if 0 /* not available yet */ #define UFFD_EVENT_FORK 0x13 -#endif /* flags for UFFD_EVENT_PAGEFAULT */ #define UFFD_PAGEFAULT_FLAG_WRITE (1<<0) /* If this was a write fault */ @@ -111,10 +108,8 @@ struct uffdio_api { * are to be considered implicitly always enabled in all kernels as * long as the uffdio_api.api requested matches UFFD_API. */ -#if 0 /* not available yet */ #define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0) #define UFFD_FEATURE_EVENT_FORK (1<<1) -#endif __u64 features; __u64 ioctls; diff -puN kernel/fork.c~userfaultfd-non-cooperative-add-fork-event kernel/fork.c --- a/kernel/fork.c~userfaultfd-non-cooperative-add-fork-event +++ a/kernel/fork.c @@ -55,6 +55,7 @@ #include <linux/rmap.h> #include <linux/ksm.h> #include <linux/acct.h> +#include <linux/userfaultfd_k.h> #include <linux/tsacct_kern.h> #include <linux/cn_proc.h> #include <linux/freezer.h> @@ -561,6 +562,7 @@ static __latent_entropy int dup_mmap(str struct rb_node **rb_link, *rb_parent; int retval; unsigned long charge; + LIST_HEAD(uf); uprobe_start_dup_mmap(); if (down_write_killable(&oldmm->mmap_sem)) { @@ -617,12 +619,13 @@ static __latent_entropy int dup_mmap(str if (retval) goto fail_nomem_policy; tmp->vm_mm = mm; + retval = dup_userfaultfd(tmp, &uf); + if (retval) + goto fail_nomem_anon_vma_fork; if (anon_vma_fork(tmp, mpnt)) goto fail_nomem_anon_vma_fork; - tmp->vm_flags &= - ~(VM_LOCKED|VM_LOCKONFAULT|VM_UFFD_MISSING|VM_UFFD_WP); + tmp->vm_flags &= ~(VM_LOCKED | VM_LOCKONFAULT); tmp->vm_next = tmp->vm_prev = NULL; - tmp->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; file = tmp->vm_file; if (file) { struct inode *inode = file_inode(file); @@ -678,6 +681,7 @@ out: up_write(&mm->mmap_sem); flush_tlb_mm(oldmm); up_write(&oldmm->mmap_sem); + dup_userfaultfd_complete(&uf); fail_uprobe_end: uprobe_end_dup_mmap(); return retval; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
