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Peter Anvin" CC: , , , , , Elliot Berman X-Mailer: b4 0.14.1 X-ClientProxiedBy: nalasex01a.na.qualcomm.com (10.47.209.196) To nasanex01b.na.qualcomm.com (10.46.141.250) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: sKUH7ABBLbjRHp9Mvo4MD33HGWJw5PK5 X-Proofpoint-GUID: sKUH7ABBLbjRHp9Mvo4MD33HGWJw5PK5 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-08-29_06,2024-08-29_02,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxlogscore=999 suspectscore=0 phishscore=0 spamscore=0 bulkscore=0 clxscore=1015 mlxscore=0 malwarescore=0 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2407110000 definitions=main-2408290158 In preparation for adding more features to KVM's guest_memfd, refactor and introduce a library which abstracts some of the core-mm decisions about managing folios associated with the file. The goal of the refactor serves two purposes: Provide an easier way to reason about memory in guest_memfd. With KVM supporting multiple confidentiality models (TDX, SEV-SNP, pKVM, ARM CCA), and coming support for allowing kernel and userspace to access this memory, it seems necessary to create a stronger abstraction between core-mm concerns and hypervisor concerns. Provide a common implementation for the various hypervisors (SEV-SNP, Gunyah, pKVM) to use. Signed-off-by: Elliot Berman --- include/linux/guest_memfd.h | 38 +++++ mm/Kconfig | 3 + mm/Makefile | 1 + mm/guest_memfd.c | 332 ++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 374 insertions(+) diff --git a/include/linux/guest_memfd.h b/include/linux/guest_memfd.h new file mode 100644 index 0000000000000..8785b7d599051 --- /dev/null +++ b/include/linux/guest_memfd.h @@ -0,0 +1,38 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved. + */ + +#ifndef _LINUX_GUEST_MEMFD_H +#define _LINUX_GUEST_MEMFD_H + +#include + +/** + * struct guest_memfd_operations - ops provided by owner to manage folios + * @invalidate_begin: called when folios should be unmapped from guest. + * May fail if folios couldn't be unmapped from guest. + * Required. + * @invalidate_end: called after invalidate_begin returns success. Optional. + * @prepare_inaccessible: called when a folio transitions to inaccessible state + * Optional. + * @release: Called when releasing the guest_memfd file. Required. + */ +struct guest_memfd_operations { + int (*invalidate_begin)(struct inode *inode, pgoff_t offset, unsigned long nr); + void (*invalidate_end)(struct inode *inode, pgoff_t offset, unsigned long nr); + int (*prepare_inaccessible)(struct inode *inode, struct folio *folio); + int (*release)(struct inode *inode); +}; + +enum guest_memfd_create_flags { + GUEST_MEMFD_FLAG_CLEAR_INACCESSIBLE = (1UL << 0), +}; + +struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags); +struct file *guest_memfd_alloc(const char *name, + const struct guest_memfd_operations *ops, + loff_t size, unsigned long flags); +bool is_guest_memfd(struct file *file, const struct guest_memfd_operations *ops); + +#endif diff --git a/mm/Kconfig b/mm/Kconfig index b72e7d040f789..333f465256957 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1168,6 +1168,9 @@ config SECRETMEM memory areas visible only in the context of the owning process and not mapped to other processes and other kernel page tables. +config GUEST_MEMFD + tristate + config ANON_VMA_NAME bool "Anonymous VMA name support" depends on PROC_FS && ADVISE_SYSCALLS && MMU diff --git a/mm/Makefile b/mm/Makefile index d2915f8c9dc01..e15a95ebeac5d 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -122,6 +122,7 @@ obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o obj-$(CONFIG_SECRETMEM) += secretmem.o +obj-$(CONFIG_GUEST_MEMFD) += guest_memfd.o obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o obj-$(CONFIG_USERFAULTFD) += userfaultfd.o obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o diff --git a/mm/guest_memfd.c b/mm/guest_memfd.c new file mode 100644 index 0000000000000..c6cd01e6064a7 --- /dev/null +++ b/mm/guest_memfd.c @@ -0,0 +1,332 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved. + */ + +#include +#include +#include +#include + +/** + * guest_memfd_grab_folio() -- grabs a folio from the guest memfd + * @file: guest memfd file to grab from + * Caller must ensure file is a guest_memfd file + * @index: the page index in the file + * @flags: bitwise OR of guest_memfd_grab_flags + * + * If a folio is returned, the folio was successfully initialized or converted + * to (in)accessible based on the GUEST_MEMFD_* flags. The folio is guaranteed + * to be (in)accessible until the folio lock is relinquished. After folio + * lock relinquished, ->prepare_inaccessible and ->prepare_accessible ops are + * responsible for preventing transitioning between the states as + * required. + * + * This function may return error even if the folio exists, in the event + * the folio couldn't be made (in)accessible as requested in the flags. + * + * This function may sleep. + * + * The caller must call either guest_memfd_put_folio() or + * guest_memfd_unsafe_folio(). + * + * Returns: + * A pointer to the grabbed folio on success, otherwise an error code. + */ +struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags) +{ + unsigned long gmem_flags = (unsigned long)file->private_data; + struct inode *inode = file_inode(file); + struct guest_memfd_operations *ops = inode->i_private; + struct folio *folio; + int r; + + /* TODO: Support huge pages. */ + folio = filemap_grab_folio(inode->i_mapping, index); + if (IS_ERR(folio)) + return folio; + + if (folio_test_uptodate(folio)) + return folio; + + folio_wait_stable(folio); + + /* + * Use the up-to-date flag to track whether or not the memory has been + * zeroed before being handed off to the guest. There is no backing + * storage for the memory, so the folio will remain up-to-date until + * it's removed. + */ + if (gmem_flags & GUEST_MEMFD_FLAG_CLEAR_INACCESSIBLE) { + unsigned long nr_pages = folio_nr_pages(folio); + unsigned long i; + + for (i = 0; i < nr_pages; i++) + clear_highpage(folio_page(folio, i)); + + } + + if (ops->prepare_inaccessible) { + r = ops->prepare_inaccessible(inode, folio); + if (r < 0) + goto out_err; + } + + folio_mark_uptodate(folio); + /* + * Ignore accessed, referenced, and dirty flags. The memory is + * unevictable and there is no storage to write back to. + */ + return folio; +out_err: + folio_unlock(folio); + folio_put(folio); + return ERR_PTR(r); +} +EXPORT_SYMBOL_GPL(guest_memfd_grab_folio); + +static long gmem_punch_hole(struct file *file, loff_t offset, loff_t len) +{ + struct inode *inode = file_inode(file); + const struct guest_memfd_operations *ops = inode->i_private; + pgoff_t start = offset >> PAGE_SHIFT; + unsigned long nr = len >> PAGE_SHIFT; + long ret; + + /* + * Bindings must be stable across invalidation to ensure the start+end + * are balanced. + */ + filemap_invalidate_lock(inode->i_mapping); + + ret = ops->invalidate_begin(inode, start, nr); + if (ret) + goto out; + + truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1); + + if (ops->invalidate_end) + ops->invalidate_end(inode, start, nr); + +out: + filemap_invalidate_unlock(inode->i_mapping); + + return 0; +} + +static long gmem_allocate(struct file *file, loff_t offset, loff_t len) +{ + struct inode *inode = file_inode(file); + struct address_space *mapping = inode->i_mapping; + pgoff_t start, index, end; + int r; + + /* Dedicated guest is immutable by default. */ + if (offset + len > i_size_read(inode)) + return -EINVAL; + + filemap_invalidate_lock_shared(mapping); + + start = offset >> PAGE_SHIFT; + end = (offset + len) >> PAGE_SHIFT; + + r = 0; + for (index = start; index < end;) { + struct folio *folio; + + if (signal_pending(current)) { + r = -EINTR; + break; + } + + folio = guest_memfd_grab_folio(file, index, 0); + if (!folio) { + r = -ENOMEM; + break; + } + + index = folio_next_index(folio); + + folio_unlock(folio); + guest_memfd_put_folio(folio, 0); + + /* 64-bit only, wrapping the index should be impossible. */ + if (WARN_ON_ONCE(!index)) + break; + + cond_resched(); + } + + filemap_invalidate_unlock_shared(mapping); + + return r; +} + +static long gmem_fallocate(struct file *file, int mode, loff_t offset, + loff_t len) +{ + int ret; + + if (!(mode & FALLOC_FL_KEEP_SIZE)) + return -EOPNOTSUPP; + + if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)) + return -EOPNOTSUPP; + + if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len)) + return -EINVAL; + + if (mode & FALLOC_FL_PUNCH_HOLE) + ret = gmem_punch_hole(file, offset, len); + else + ret = gmem_allocate(file, offset, len); + + if (!ret) + file_modified(file); + return ret; +} + +static int gmem_release(struct inode *inode, struct file *file) +{ + struct guest_memfd_operations *ops = inode->i_private; + + return ops->release(inode); +} + +static const struct file_operations gmem_fops = { + .open = generic_file_open, + .llseek = generic_file_llseek, + .release = gmem_release, + .fallocate = gmem_fallocate, + .owner = THIS_MODULE, +}; + +static int gmem_migrate_folio(struct address_space *mapping, struct folio *dst, + struct folio *src, enum migrate_mode mode) +{ + WARN_ON_ONCE(1); + return -EINVAL; +} + +static int gmem_error_folio(struct address_space *mapping, struct folio *folio) +{ + struct inode *inode = mapping->host; + struct guest_memfd_operations *ops = inode->i_private; + off_t offset = folio->index; + size_t nr = folio_nr_pages(folio); + int ret; + + filemap_invalidate_lock_shared(mapping); + + ret = ops->invalidate_begin(inode, offset, nr); + if (!ret && ops->invalidate_end) + ops->invalidate_end(inode, offset, nr); + + filemap_invalidate_unlock_shared(mapping); + + return ret; +} + +static bool gmem_release_folio(struct folio *folio, gfp_t gfp) +{ + struct inode *inode = folio_inode(folio); + struct guest_memfd_operations *ops = inode->i_private; + off_t offset = folio->index; + size_t nr = folio_nr_pages(folio); + int ret; + + ret = ops->invalidate_begin(inode, offset, nr); + if (ret) + return false; + if (ops->invalidate_end) + ops->invalidate_end(inode, offset, nr); + + return true; +} + +static const struct address_space_operations gmem_aops = { + .dirty_folio = noop_dirty_folio, + .migrate_folio = gmem_migrate_folio, + .error_remove_folio = gmem_error_folio, + .release_folio = gmem_release_folio, +}; + +static inline bool guest_memfd_check_ops(const struct guest_memfd_operations *ops) +{ + return ops->invalidate_begin && ops->release; +} + +static inline unsigned long guest_memfd_valid_flags(void) +{ + return GUEST_MEMFD_FLAG_CLEAR_INACCESSIBLE; +} + +/** + * guest_memfd_alloc() - Create a guest_memfd file + * @name: the name of the new file + * @ops: operations table for the guest_memfd file + * @size: the size of the file + * @flags: flags controlling behavior of the file + * + * Creates a new guest_memfd file. + */ +struct file *guest_memfd_alloc(const char *name, + const struct guest_memfd_operations *ops, + loff_t size, unsigned long flags) +{ + struct inode *inode; + struct file *file; + + if (size <= 0 || !PAGE_ALIGNED(size)) + return ERR_PTR(-EINVAL); + + if (!guest_memfd_check_ops(ops)) + return ERR_PTR(-EINVAL); + + if (flags & ~guest_memfd_valid_flags()) + return ERR_PTR(-EINVAL); + + /* + * Use the so called "secure" variant, which creates a unique inode + * instead of reusing a single inode. Each guest_memfd instance needs + * its own inode to track the size, flags, etc. + */ + file = anon_inode_create_getfile(name, &gmem_fops, (void *)flags, + O_RDWR, NULL); + if (IS_ERR(file)) + return file; + + file->f_flags |= O_LARGEFILE; + + inode = file_inode(file); + WARN_ON(file->f_mapping != inode->i_mapping); + + inode->i_private = (void *)ops; /* discards const qualifier */ + inode->i_mapping->a_ops = &gmem_aops; + inode->i_mode |= S_IFREG; + inode->i_size = size; + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); + mapping_set_inaccessible(inode->i_mapping); + /* Unmovable mappings are supposed to be marked unevictable as well. */ + WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); + + return file; +} +EXPORT_SYMBOL_GPL(guest_memfd_alloc); + +/** + * is_guest_memfd() - Returns true if the struct file is a guest_memfd + * @file: the file to check + * @ops: the expected operations table + */ +bool is_guest_memfd(struct file *file, const struct guest_memfd_operations *ops) +{ + if (file->f_op != &gmem_fops) + return false; + + struct inode *inode = file_inode(file); + struct guest_memfd_operations *gops = inode->i_private; + + return ops == gops; +} +EXPORT_SYMBOL_GPL(is_guest_memfd);