vhost/vsock: Use kvmalloc/kvfree for larger packets.

In the Linux kernel, the following vulnerability has been resolved:

vhost/vsock: Use kvmalloc/kvfree for larger packets.

When copying a large file over sftp over vsock, data size is usually 32kB,

and kmalloc seems to fail to try to allocate 32 32kB regions.

vhost-5837: page allocation failure: order:4, mode:0x24040c0

Call Trace:

[<ffffffffb6a0df64>] dump_stack+0x97/0xdb

[<ffffffffb68d6aed>] warn_alloc_failed+0x10f/0x138

[<ffffffffb68d868a>] ? __alloc_pages_direct_compact+0x38/0xc8

[<ffffffffb664619f>] __alloc_pages_nodemask+0x84c/0x90d

[<ffffffffb6646e56>] alloc_kmem_pages+0x17/0x19

[<ffffffffb6653a26>] kmalloc_order_trace+0x2b/0xdb

[<ffffffffb66682f3>] __kmalloc+0x177/0x1f7

[<ffffffffb66e0d94>] ? copy_from_iter+0x8d/0x31d

[<ffffffffc0689ab7>] vhost_vsock_handle_tx_kick+0x1fa/0x301 [vhost_vsock]

[<ffffffffc06828d9>] vhost_worker+0xf7/0x157 [vhost]

[<ffffffffb683ddce>] kthread+0xfd/0x105

[<ffffffffc06827e2>] ? vhost_dev_set_owner+0x22e/0x22e [vhost]

[<ffffffffb683dcd1>] ? flush_kthread_worker+0xf3/0xf3

[<ffffffffb6eb332e>] ret_from_fork+0x4e/0x80

[<ffffffffb683dcd1>] ? flush_kthread_worker+0xf3/0xf3

Work around by doing kvmalloc instead.