qemu/hw/dataplane/vring.c

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/* Copyright 2012 Red Hat, Inc.
* Copyright IBM, Corp. 2012
*
* Based on Linux 2.6.39 vhost code:
* Copyright (C) 2009 Red Hat, Inc.
* Copyright (C) 2006 Rusty Russell IBM Corporation
*
* Author: Michael S. Tsirkin <mst@redhat.com>
* Stefan Hajnoczi <stefanha@redhat.com>
*
* Inspiration, some code, and most witty comments come from
* Documentation/virtual/lguest/lguest.c, by Rusty Russell
*
* This work is licensed under the terms of the GNU GPL, version 2.
*/
#include "trace.h"
#include "vring.h"
#include "qemu/error-report.h"
/* Map the guest's vring to host memory */
bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
{
hwaddr vring_addr = virtio_queue_get_ring_addr(vdev, n);
hwaddr vring_size = virtio_queue_get_ring_size(vdev, n);
void *vring_ptr;
vring->broken = false;
hostmem_init(&vring->hostmem);
vring_ptr = hostmem_lookup(&vring->hostmem, vring_addr, vring_size, true);
if (!vring_ptr) {
error_report("Failed to map vring "
"addr %#" HWADDR_PRIx " size %" HWADDR_PRIu,
vring_addr, vring_size);
vring->broken = true;
return false;
}
vring_init(&vring->vr, virtio_queue_get_num(vdev, n), vring_ptr, 4096);
vring->last_avail_idx = 0;
vring->last_used_idx = 0;
vring->signalled_used = 0;
vring->signalled_used_valid = false;
trace_vring_setup(virtio_queue_get_ring_addr(vdev, n),
vring->vr.desc, vring->vr.avail, vring->vr.used);
return true;
}
void vring_teardown(Vring *vring)
{
hostmem_finalize(&vring->hostmem);
}
/* Disable guest->host notifies */
void vring_disable_notification(VirtIODevice *vdev, Vring *vring)
{
if (!(vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX))) {
vring->vr.used->flags |= VRING_USED_F_NO_NOTIFY;
}
}
/* Enable guest->host notifies
*
* Return true if the vring is empty, false if there are more requests.
*/
bool vring_enable_notification(VirtIODevice *vdev, Vring *vring)
{
if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
vring_avail_event(&vring->vr) = vring->vr.avail->idx;
} else {
vring->vr.used->flags &= ~VRING_USED_F_NO_NOTIFY;
}
smp_mb(); /* ensure update is seen before reading avail_idx */
return !vring_more_avail(vring);
}
/* This is stolen from linux/drivers/vhost/vhost.c:vhost_notify() */
bool vring_should_notify(VirtIODevice *vdev, Vring *vring)
{
uint16_t old, new;
bool v;
/* Flush out used index updates. This is paired
* with the barrier that the Guest executes when enabling
* interrupts. */
smp_mb();
if ((vdev->guest_features & VIRTIO_F_NOTIFY_ON_EMPTY) &&
unlikely(vring->vr.avail->idx == vring->last_avail_idx)) {
return true;
}
if (!(vdev->guest_features & VIRTIO_RING_F_EVENT_IDX)) {
return !(vring->vr.avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
}
old = vring->signalled_used;
v = vring->signalled_used_valid;
new = vring->signalled_used = vring->last_used_idx;
vring->signalled_used_valid = true;
if (unlikely(!v)) {
return true;
}
return vring_need_event(vring_used_event(&vring->vr), new, old);
}
/* This is stolen from linux/drivers/vhost/vhost.c. */
static int get_indirect(Vring *vring,
struct iovec iov[], struct iovec *iov_end,
unsigned int *out_num, unsigned int *in_num,
struct vring_desc *indirect)
{
struct vring_desc desc;
unsigned int i = 0, count, found = 0;
/* Sanity check */
if (unlikely(indirect->len % sizeof(desc))) {
error_report("Invalid length in indirect descriptor: "
"len %#x not multiple of %#zx",
indirect->len, sizeof(desc));
vring->broken = true;
return -EFAULT;
}
count = indirect->len / sizeof(desc);
/* Buffers are chained via a 16 bit next field, so
* we can have at most 2^16 of these. */
if (unlikely(count > USHRT_MAX + 1)) {
error_report("Indirect buffer length too big: %d", indirect->len);
vring->broken = true;
return -EFAULT;
}
do {
struct vring_desc *desc_ptr;
/* Translate indirect descriptor */
desc_ptr = hostmem_lookup(&vring->hostmem,
indirect->addr + found * sizeof(desc),
sizeof(desc), false);
if (!desc_ptr) {
error_report("Failed to map indirect descriptor "
"addr %#" PRIx64 " len %zu",
(uint64_t)indirect->addr + found * sizeof(desc),
sizeof(desc));
vring->broken = true;
return -EFAULT;
}
desc = *desc_ptr;
/* Ensure descriptor has been loaded before accessing fields */
barrier(); /* read_barrier_depends(); */
if (unlikely(++found > count)) {
error_report("Loop detected: last one at %u "
"indirect size %u", i, count);
vring->broken = true;
return -EFAULT;
}
if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
error_report("Nested indirect descriptor");
vring->broken = true;
return -EFAULT;
}
/* Stop for now if there are not enough iovecs available. */
if (iov >= iov_end) {
return -ENOBUFS;
}
iov->iov_base = hostmem_lookup(&vring->hostmem, desc.addr, desc.len,
desc.flags & VRING_DESC_F_WRITE);
if (!iov->iov_base) {
error_report("Failed to map indirect descriptor"
"addr %#" PRIx64 " len %u",
(uint64_t)desc.addr, desc.len);
vring->broken = true;
return -EFAULT;
}
iov->iov_len = desc.len;
iov++;
/* If this is an input descriptor, increment that count. */
if (desc.flags & VRING_DESC_F_WRITE) {
*in_num += 1;
} else {
/* If it's an output descriptor, they're all supposed
* to come before any input descriptors. */
if (unlikely(*in_num)) {
error_report("Indirect descriptor "
"has out after in: idx %u", i);
vring->broken = true;
return -EFAULT;
}
*out_num += 1;
}
i = desc.next;
} while (desc.flags & VRING_DESC_F_NEXT);
return 0;
}
/* This looks in the virtqueue and for the first available buffer, and converts
* it to an iovec for convenient access. Since descriptors consist of some
* number of output then some number of input descriptors, it's actually two
* iovecs, but we pack them into one and note how many of each there were.
*
* This function returns the descriptor number found, or vq->num (which is
* never a valid descriptor number) if none was found. A negative code is
* returned on error.
*
* Stolen from linux/drivers/vhost/vhost.c.
*/
int vring_pop(VirtIODevice *vdev, Vring *vring,
struct iovec iov[], struct iovec *iov_end,
unsigned int *out_num, unsigned int *in_num)
{
struct vring_desc desc;
unsigned int i, head, found = 0, num = vring->vr.num;
uint16_t avail_idx, last_avail_idx;
/* If there was a fatal error then refuse operation */
if (vring->broken) {
return -EFAULT;
}
/* Check it isn't doing very strange things with descriptor numbers. */
last_avail_idx = vring->last_avail_idx;
avail_idx = vring->vr.avail->idx;
barrier(); /* load indices now and not again later */
if (unlikely((uint16_t)(avail_idx - last_avail_idx) > num)) {
error_report("Guest moved used index from %u to %u",
last_avail_idx, avail_idx);
vring->broken = true;
return -EFAULT;
}
/* If there's nothing new since last we looked. */
if (avail_idx == last_avail_idx) {
return -EAGAIN;
}
/* Only get avail ring entries after they have been exposed by guest. */
smp_rmb();
/* Grab the next descriptor number they're advertising, and increment
* the index we've seen. */
head = vring->vr.avail->ring[last_avail_idx % num];
/* If their number is silly, that's an error. */
if (unlikely(head >= num)) {
error_report("Guest says index %u > %u is available", head, num);
vring->broken = true;
return -EFAULT;
}
if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
vring_avail_event(&vring->vr) = vring->vr.avail->idx;
}
/* When we start there are none of either input nor output. */
*out_num = *in_num = 0;
i = head;
do {
if (unlikely(i >= num)) {
error_report("Desc index is %u > %u, head = %u", i, num, head);
vring->broken = true;
return -EFAULT;
}
if (unlikely(++found > num)) {
error_report("Loop detected: last one at %u vq size %u head %u",
i, num, head);
vring->broken = true;
return -EFAULT;
}
desc = vring->vr.desc[i];
/* Ensure descriptor is loaded before accessing fields */
barrier();
if (desc.flags & VRING_DESC_F_INDIRECT) {
int ret = get_indirect(vring, iov, iov_end, out_num, in_num, &desc);
if (ret < 0) {
return ret;
}
continue;
}
/* If there are not enough iovecs left, stop for now. The caller
* should check if there are more descs available once they have dealt
* with the current set.
*/
if (iov >= iov_end) {
return -ENOBUFS;
}
/* TODO handle non-contiguous memory across region boundaries */
iov->iov_base = hostmem_lookup(&vring->hostmem, desc.addr, desc.len,
desc.flags & VRING_DESC_F_WRITE);
if (!iov->iov_base) {
error_report("Failed to map vring desc addr %#" PRIx64 " len %u",
(uint64_t)desc.addr, desc.len);
vring->broken = true;
return -EFAULT;
}
iov->iov_len = desc.len;
iov++;
if (desc.flags & VRING_DESC_F_WRITE) {
/* If this is an input descriptor,
* increment that count. */
*in_num += 1;
} else {
/* If it's an output descriptor, they're all supposed
* to come before any input descriptors. */
if (unlikely(*in_num)) {
error_report("Descriptor has out after in: idx %d", i);
vring->broken = true;
return -EFAULT;
}
*out_num += 1;
}
i = desc.next;
} while (desc.flags & VRING_DESC_F_NEXT);
/* On success, increment avail index. */
vring->last_avail_idx++;
return head;
}
/* After we've used one of their buffers, we tell them about it.
*
* Stolen from linux/drivers/vhost/vhost.c.
*/
void vring_push(Vring *vring, unsigned int head, int len)
{
struct vring_used_elem *used;
uint16_t new;
/* Don't touch vring if a fatal error occurred */
if (vring->broken) {
return;
}
/* The virtqueue contains a ring of used buffers. Get a pointer to the
* next entry in that used ring. */
used = &vring->vr.used->ring[vring->last_used_idx % vring->vr.num];
used->id = head;
used->len = len;
/* Make sure buffer is written before we update index. */
smp_wmb();
new = vring->vr.used->idx = ++vring->last_used_idx;
if (unlikely((int16_t)(new - vring->signalled_used) < (uint16_t)1)) {
vring->signalled_used_valid = false;
}
}