Re: [PATCH v3 1/2] virtiofs: use pages instead of pointer for kernel direct IO

[Hou Tao <houtao@huaweicloud.com>]

On 4/26/2024 10:39 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
>
> 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+ #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:
>

SNIP
> @@ -1585,7 +1589,7 @@ 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;

Just find out that flush_kernel_vmap_range() and
invalidate_kernel_vmap_range() should be used before DMA rw operation
and after DMA read operation if the kvec IO is backed by vmalloc() area.
Will update it in v4.
>  
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index f239196103137..d4f04e19058c1 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -860,6 +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;
>  
> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> index 322af827a2329..36984c0e23d14 100644
> --- a/fs/fuse/virtio_fs.c
> +++ b/fs/fuse/virtio_fs.c
> @@ -1512,6 +1512,7 @@ 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,