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virtiofs: use pages instead of pointer for kernel direct IO
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When trying to insert a 10MB kernel module kept in a virtio-fs with cache
disabled, the following warning was reported:

  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 404 at mm/page_alloc.c:4551 ......
  Modules linked in:
  CPU: 1 PID: 404 Comm: insmod Not tainted 6.9.0-rc5+ torvalds#123
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ......
  RIP: 0010:__alloc_pages+0x2bf/0x380
  ......
  Call Trace:
   <TASK>
   ? __warn+0x8e/0x150
   ? __alloc_pages+0x2bf/0x380
   __kmalloc_large_node+0x86/0x160
   __kmalloc+0x33c/0x480
   virtio_fs_enqueue_req+0x240/0x6d0
   virtio_fs_wake_pending_and_unlock+0x7f/0x190
   queue_request_and_unlock+0x55/0x60
   fuse_simple_request+0x152/0x2b0
   fuse_direct_io+0x5d2/0x8c0
   fuse_file_read_iter+0x121/0x160
   __kernel_read+0x151/0x2d0
   kernel_read+0x45/0x50
   kernel_read_file+0x1a9/0x2a0
   init_module_from_file+0x6a/0xe0
   idempotent_init_module+0x175/0x230
   __x64_sys_finit_module+0x5d/0xb0
   x64_sys_call+0x1c3/0x9e0
   do_syscall_64+0x3d/0xc0
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
   ......
   </TASK>
  ---[ end trace 0000000000000000 ]---

The warning is triggered as follows:

1) syscall finit_module() handles the module insertion and it invokes
kernel_read_file() to read the content of the module first.

2) kernel_read_file() allocates a 10MB buffer by using vmalloc() and
passes it to kernel_read(). kernel_read() constructs a kvec iter by
using iov_iter_kvec() and passes it to fuse_file_read_iter().

3) virtio-fs disables the cache, so fuse_file_read_iter() invokes
fuse_direct_io(). As for now, the maximal read size for kvec iter is
only limited by fc->max_read. For virtio-fs, max_read is UINT_MAX, so
fuse_direct_io() doesn't split the 10MB buffer. It saves the address and
the size of the 10MB-sized buffer in out_args[0] of a fuse request and
passes the fuse request to virtio_fs_wake_pending_and_unlock().

4) virtio_fs_wake_pending_and_unlock() uses virtio_fs_enqueue_req() to
queue the request. Because virtiofs need DMA-able address, so
virtio_fs_enqueue_req() uses kmalloc() to allocate a bounce buffer for
all fuse args, copies these args into the bounce buffer and passed the
physical address of the bounce buffer to virtiofsd. The total length of
these fuse args for the passed fuse request is about 10MB, so
copy_args_to_argbuf() invokes kmalloc() with a 10MB size parameter and
it triggers the warning in __alloc_pages():

	if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp))
		return NULL;

5) virtio_fs_enqueue_req() will retry the memory allocation in a
kworker, but it won't help, because kmalloc() will always return NULL
due to the abnormal size and finit_module() will hang forever.

A feasible solution is to limit the value of max_read for virtio-fs, so
the length passed to kmalloc() will be limited. However it will affect
the maximal read size for normal read. And for virtio-fs write initiated
from kernel, it has the similar problem but now there is no way to limit
fc->max_write in kernel.

So instead of limiting both the values of max_read and max_write in
kernel, introducing use_pages_for_kvec_io in fuse_conn and setting it as
true in virtiofs. When use_pages_for_kvec_io is enabled, fuse will use
pages instead of pointer to pass the KVEC_IO data.

After switching to pages for KVEC_IO data, these pages will be used for
DMA through virtio-fs. If these pages are backed by vmalloc(),
{flush|invalidate}_kernel_vmap_range() are necessary to flush or
invalidate the cache before the DMA operation. So add two new fields in
fuse_args_pages to record the base address of vmalloc area and the
condition indicating whether invalidation is needed. Perform the flush
in fuse_get_user_pages() for write operations and the invalidation in
fuse_release_user_pages() for read operations.

It may seem necessary to introduce another field in fuse_conn to
indicate that these KVEC_IO pages are used for DMA, However, considering
that virtio-fs is currently the only user of use_pages_for_kvec_io, just
reuse use_pages_for_kvec_io to indicate that these pages will be used
for DMA.

Fixes: a62a8ef ("virtio-fs: add virtiofs filesystem")
Signed-off-by: Hou Tao <[email protected]>
Tested-by: Jingbo Xu <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>
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Hou Tao authored and Miklos Szeredi committed Oct 15, 2024
1 parent 8e51b65 commit a60f578
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Showing 3 changed files with 50 additions and 19 deletions.
62 changes: 43 additions & 19 deletions fs/fuse/file.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -645,7 +645,7 @@ void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
args->out_args[0].size = count;
}

static void fuse_release_user_pages(struct fuse_args_pages *ap,
static void fuse_release_user_pages(struct fuse_args_pages *ap, ssize_t nres,
bool should_dirty)
{
unsigned int i;
Expand All @@ -656,6 +656,9 @@ static void fuse_release_user_pages(struct fuse_args_pages *ap,
if (ap->args.is_pinned)
unpin_user_page(ap->pages[i]);
}

if (nres > 0 && ap->args.invalidate_vmap)
invalidate_kernel_vmap_range(ap->args.vmap_base, nres);
}

static void fuse_io_release(struct kref *kref)
Expand Down Expand Up @@ -754,25 +757,29 @@ static void fuse_aio_complete_req(struct fuse_mount *fm, struct fuse_args *args,
struct fuse_io_args *ia = container_of(args, typeof(*ia), ap.args);
struct fuse_io_priv *io = ia->io;
ssize_t pos = -1;

fuse_release_user_pages(&ia->ap, io->should_dirty);
size_t nres;

if (err) {
/* Nothing */
} else if (io->write) {
if (ia->write.out.size > ia->write.in.size) {
err = -EIO;
} else if (ia->write.in.size != ia->write.out.size) {
pos = ia->write.in.offset - io->offset +
ia->write.out.size;
} else {
nres = ia->write.out.size;
if (ia->write.in.size != ia->write.out.size)
pos = ia->write.in.offset - io->offset +
ia->write.out.size;
}
} else {
u32 outsize = args->out_args[0].size;

nres = outsize;
if (ia->read.in.size != outsize)
pos = ia->read.in.offset - io->offset + outsize;
}

fuse_release_user_pages(&ia->ap, err ?: nres, io->should_dirty);

fuse_aio_complete(io, err, pos);
fuse_io_free(ia);
}
Expand Down Expand Up @@ -1468,24 +1475,37 @@ static inline size_t fuse_get_frag_size(const struct iov_iter *ii,

static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
size_t *nbytesp, int write,
unsigned int max_pages)
unsigned int max_pages,
bool use_pages_for_kvec_io)
{
bool flush_or_invalidate = false;
size_t nbytes = 0; /* # bytes already packed in req */
ssize_t ret = 0;

/* Special case for kernel I/O: can copy directly into the buffer */
/* Special case for kernel I/O: can copy directly into the buffer.
* However if the implementation of fuse_conn requires pages instead of
* pointer (e.g., virtio-fs), use iov_iter_extract_pages() instead.
*/
if (iov_iter_is_kvec(ii)) {
unsigned long user_addr = fuse_get_user_addr(ii);
size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
void *user_addr = (void *)fuse_get_user_addr(ii);

if (write)
ap->args.in_args[1].value = (void *) user_addr;
else
ap->args.out_args[0].value = (void *) user_addr;
if (!use_pages_for_kvec_io) {
size_t frag_size = fuse_get_frag_size(ii, *nbytesp);

iov_iter_advance(ii, frag_size);
*nbytesp = frag_size;
return 0;
if (write)
ap->args.in_args[1].value = user_addr;
else
ap->args.out_args[0].value = user_addr;

iov_iter_advance(ii, frag_size);
*nbytesp = frag_size;
return 0;
}

if (is_vmalloc_addr(user_addr)) {
ap->args.vmap_base = user_addr;
flush_or_invalidate = true;
}
}

while (nbytes < *nbytesp && ap->num_pages < max_pages) {
Expand Down Expand Up @@ -1514,6 +1534,10 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
(PAGE_SIZE - ret) & (PAGE_SIZE - 1);
}

if (write && flush_or_invalidate)
flush_kernel_vmap_range(ap->args.vmap_base, nbytes);

ap->args.invalidate_vmap = !write && flush_or_invalidate;
ap->args.is_pinned = iov_iter_extract_will_pin(ii);
ap->args.user_pages = true;
if (write)
Expand Down Expand Up @@ -1582,7 +1606,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
size_t nbytes = min(count, nmax);

err = fuse_get_user_pages(&ia->ap, iter, &nbytes, write,
max_pages);
max_pages, fc->use_pages_for_kvec_io);
if (err && !nbytes)
break;

Expand All @@ -1596,7 +1620,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
}

if (!io->async || nres < 0) {
fuse_release_user_pages(&ia->ap, io->should_dirty);
fuse_release_user_pages(&ia->ap, nres, io->should_dirty);
fuse_io_free(ia);
}
ia = NULL;
Expand Down
6 changes: 6 additions & 0 deletions fs/fuse/fuse_i.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -309,9 +309,12 @@ struct fuse_args {
bool may_block:1;
bool is_ext:1;
bool is_pinned:1;
bool invalidate_vmap:1;
struct fuse_in_arg in_args[3];
struct fuse_arg out_args[2];
void (*end)(struct fuse_mount *fm, struct fuse_args *args, int error);
/* Used for kvec iter backed by vmalloc address */
void *vmap_base;
};

struct fuse_args_pages {
Expand Down Expand Up @@ -857,6 +860,9 @@ struct fuse_conn {
/** Passthrough support for read/write IO */
unsigned int passthrough:1;

/* Use pages instead of pointer for kernel I/O */
unsigned int use_pages_for_kvec_io:1;

/** Maximum stack depth for passthrough backing files */
int max_stack_depth;

Expand Down
1 change: 1 addition & 0 deletions fs/fuse/virtio_fs.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1691,6 +1691,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
fc->delete_stale = true;
fc->auto_submounts = true;
fc->sync_fs = true;
fc->use_pages_for_kvec_io = true;

/* Tell FUSE to split requests that exceed the virtqueue's size */
fc->max_pages_limit = min_t(unsigned int, fc->max_pages_limit,
Expand Down

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