On Wed, Dec 05, 2012 at 03:37:02PM +0100, Sjur Brændeland wrote:
> Isolate the access to user-memory in separate inline
> functions. This open up for reuse from host-side virtioqueue
> implementation accessing virtio-ring in kernel space.
>
> Signed-off-by: Sjur Brændeland <[email protected]>
> ---
> drivers/virtio/virtio_ring_host.c | 81
> ++++++++++++++++++++++++++-----------
> 1 files changed, 57 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring_host.c
> b/drivers/virtio/virtio_ring_host.c
> index 192b838..0750099 100644
> --- a/drivers/virtio/virtio_ring_host.c
> +++ b/drivers/virtio/virtio_ring_host.c
> @@ -18,44 +18,45 @@
> #include <linux/virtio_ring.h>
> #include <linux/module.h>
> #include <linux/uaccess.h>
> +#include <linux/kconfig.h>
>
> MODULE_LICENSE("GPL");
>
> -struct vring_used_elem *vring_add_used_user(struct vring_host *vh,
> - unsigned int head, int len)
> +
> +static inline struct vring_used_elem *_vring_add_used(struct vring_host *vh,
> + u32 head, u32 len,
> + bool (*cpy)(void *dst,
> + void *src,
> + size_t s),
> + void (*wbarrier)(void))
> {
> struct vring_used_elem *used;
> + u16 last_used;
>
> /* The virtqueue contains a ring of used buffers. Get a pointer to the
> * next entry in that used ring. */
> - used = &vh->vr.used->ring[vh->last_used_idx % vh->vr.num];
> - if (__put_user(head, &used->id)) {
> - pr_debug("Failed to write used id");
> + used = &vh->vr.used->ring[vh->last_used_idx & (vh->vr.num - 1)];
> + if (!cpy(&used->id, &head, sizeof(used->id)) ||
> + !cpy(&used->len, &len, sizeof(used->len)))
> return NULL;
> - }
> - if (__put_user(len, &used->len)) {
> - pr_debug("Failed to write used len");
> + wbarrier();
> + last_used = vh->last_used_idx + 1;
> + if (!cpy(&vh->vr.used->idx, &last_used, sizeof(vh->vr.used->idx)))
> return NULL;
I think this is broken: we need a 16 bit access, this is
doing a memcpy which is byte by byte.
> - }
> - /* Make sure buffer is written before we update index. */
> - smp_wmb();
> - if (__put_user(vh->last_used_idx + 1, &vh->vr.used->idx)) {
> - pr_debug("Failed to increment used idx");
> - return NULL;
> - }
> - vh->last_used_idx++;
> + vh->last_used_idx = last_used;
> return used;
> }
> -EXPORT_SYMBOL(vring_add_used_user);
>
> -int vring_avail_desc_user(struct vring_host *vh)
> +static inline int _vring_avail_desc(struct vring_host *vh,
> + bool (*get)(u16 *dst, u16 *src),
> + void (*read_barrier)(void))
> {
> - int head;
> + u16 head;
> u16 last_avail_idx;
>
> /* Check it isn't doing very strange things with descriptor numbers. */
> last_avail_idx = vh->last_avail_idx;
> - if (unlikely(__get_user(vh->avail_idx, &vh->vr.avail->idx))) {
> + if (unlikely(!get(&vh->avail_idx, &vh->vr.avail->idx))) {
> pr_debug("Failed to access avail idx at %p\n",
> &vh->vr.avail->idx);
> return -EFAULT;
> @@ -69,13 +70,12 @@ int vring_avail_desc_user(struct vring_host *vh)
> return vh->vr.num;
>
> /* Only get avail ring entries after they have been exposed by guest. */
> - smp_rmb();
> + read_barrier();
>
> /* Grab the next descriptor number they're advertising, and increment
> * the index we've seen. */
> - if (unlikely(__get_user(head,
> - &vh->vr.avail->ring[last_avail_idx %
> - vh->vr.num]))) {
> + if (unlikely(!get(&head, &vh->vr.avail->ring[last_avail_idx &
> + (vh->vr.num - 1)]))) {
> pr_debug("Failed to read head: idx %d address %p\n",
> last_avail_idx,
> &vh->vr.avail->ring[last_avail_idx %
> @@ -92,6 +92,39 @@ int vring_avail_desc_user(struct vring_host *vh)
>
> return head;
> }
> +
> +static inline void smp_write_barrier(void)
> +{
> + smp_wmb();
> +}
> +
> +static inline void smp_read_barrier(void)
> +{
> + smp_rmb();
> +}
> +
> +static inline bool userspace_cpy_to(void *dst, void *src, size_t s)
> +{
> + return __copy_to_user(dst, src, s) == 0;
> +}
> +
> +static inline bool userspace_get(u16 *dst, u16 *src)
> +{
> + return __get_user(*dst, src);
> +}
> +
> +struct vring_used_elem *vring_add_used_user(struct vring_host *vh,
> + unsigned int head, int len)
> +{
> + return _vring_add_used(vh, head, len, userspace_cpy_to,
> + smp_write_barrier);
> +}
> +EXPORT_SYMBOL(vring_add_used_user);
> +
> +int vring_avail_desc_user(struct vring_host *vh)
> +{
> + return _vring_avail_desc(vh, userspace_get, smp_read_barrier);
> +}
> EXPORT_SYMBOL(vring_avail_desc_user);
>
> /* Each buffer in the virtqueues is actually a chain of descriptors. This
> --
> 1.7.5.4
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