On 2019/12/18 下午5:19, Herbert Xu wrote:
Will Deacon <[email protected]> wrote:
--->8
// drivers/vhost/vhost.c
static int get_indirect(struct vhost_virtqueue *vq,
struct iovec iov[], unsigned int iov_size,
unsigned int *out_num, unsigned int *in_num,
struct vhost_log *log, unsigned int *log_num,
struct vring_desc *indirect)
{
[...]
/* We will use the result as an address to read from, so most
* architectures only need a compiler barrier here. */
read_barrier_depends();
--->8
Unfortunately, although the barrier is commented (hurrah!), it's not
particularly enlightening about the accesses making up the dependency
chain, and I don't understand the supposed need for a compiler barrier
either (read_barrier_depends() doesn't generally provide this).
Does anybody know which accesses are being ordered here? Usually you'd need
a READ_ONCE()/rcu_dereference() beginning the chain, but I haven't managed
to find one...
I think what it's trying to separate is using indirect->addr as a
base and then reading from that through copy_from_iter.
Cheers,
The question is that there's a smp_rmb() before in vhost_get_vq_desc(),
isn't it sufficient to do this?
Thanks
_______________________________________________
Virtualization mailing list
[email protected]
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
