xref: /kvmtool/virtio/core.c (revision 1382aba018748f7d2494ab2e22d51ff91939e3e4)

#include <linux/virtio_ring.h>
#include <linux/types.h>
#include <sys/uio.h>

#include "kvm/barrier.h"

#include "kvm/kvm.h"
#include "kvm/virtio.h"

struct vring_used_elem *virt_queue__set_used_elem(struct virt_queue *queue, u32 head, u32 len)
{
	struct vring_used_elem *used_elem;

	used_elem	= &queue->vring.used->ring[queue->vring.used->idx % queue->vring.num];
	used_elem->id	= head;
	used_elem->len	= len;

	/*
	 * Use wmb to assure that used elem was updated with head and len.
	 * We need a wmb here since we can't advance idx unless we're ready
	 * to pass the used element to the guest.
	 */
	wmb();
	queue->vring.used->idx++;

	/*
	 * Use wmb to assure used idx has been increased before we signal the guest.
	 * Without a wmb here the guest may ignore the queue since it won't see
	 * an updated idx.
	 */
	wmb();

	return used_elem;
}

/*
 * Each buffer in the virtqueues is actually a chain of descriptors.  This
 * function returns the next descriptor in the chain, or vq->vring.num if we're
 * at the end.
 */
static unsigned next_desc(struct vring_desc *desc,
			  unsigned int i, unsigned int max)
{
	unsigned int next;

	/* If this descriptor says it doesn't chain, we're done. */
	if (!(desc[i].flags & VRING_DESC_F_NEXT))
		return max;

	/* Check they're not leading us off end of descriptors. */
	next = desc[i].next;
	/* Make sure compiler knows to grab that: we don't want it changing! */
	wmb();

	return next;
}

u16 virt_queue__get_head_iov(struct virt_queue *vq, struct iovec iov[], u16 *out, u16 *in, u16 head, struct kvm *kvm)
{
	struct vring_desc *desc;
	u16 idx;
	u16 max;

	idx = head;
	*out = *in = 0;
	max = vq->vring.num;
	desc = vq->vring.desc;

	if (desc[idx].flags & VRING_DESC_F_INDIRECT) {

		max = desc[idx].len / sizeof(struct vring_desc);
		desc = guest_flat_to_host(kvm, desc[idx].addr);
		idx = 0;
	}

	do {
		/* Grab the first descriptor, and check it's OK. */
		iov[*out + *in].iov_len = desc[idx].len;
		iov[*out + *in].iov_base = guest_flat_to_host(kvm, desc[idx].addr);
		/* If this is an input descriptor, increment that count. */
		if (desc[idx].flags & VRING_DESC_F_WRITE)
			(*in)++;
		else
			(*out)++;
	} while ((idx = next_desc(desc, idx, max)) != max);

	return head;
}

u16 virt_queue__get_iov(struct virt_queue *vq, struct iovec iov[], u16 *out, u16 *in, struct kvm *kvm)
{
	u16 head;

	head = virt_queue__pop(vq);

	return virt_queue__get_head_iov(vq, iov, out, in, head, kvm);
}

/* in and out are relative to guest */
u16 virt_queue__get_inout_iov(struct kvm *kvm, struct virt_queue *queue,
			      struct iovec in_iov[], struct iovec out_iov[],
			      u16 *in, u16 *out)
{
	struct vring_desc *desc;
	u16 head, idx;

	idx = head = virt_queue__pop(queue);
	*out = *in = 0;
	do {
		desc = virt_queue__get_desc(queue, idx);
		if (desc->flags & VRING_DESC_F_WRITE) {
			in_iov[*in].iov_base = guest_flat_to_host(kvm,
								  desc->addr);
			in_iov[*in].iov_len = desc->len;
			(*in)++;
		} else {
			out_iov[*out].iov_base = guest_flat_to_host(kvm,
								    desc->addr);
			out_iov[*out].iov_len = desc->len;
			(*out)++;
		}
		if (desc->flags & VRING_DESC_F_NEXT)
			idx = desc->next;
		else
			break;
	} while (1);

	return head;
}

int virtio__get_dev_specific_field(int offset, bool msix, u32 *config_off)
{
	if (msix) {
		if (offset < 4)
			return VIRTIO_PCI_O_MSIX;
		else
			offset -= 4;
	}

	*config_off = offset;

	return VIRTIO_PCI_O_CONFIG;
}

bool virtio_queue__should_signal(struct virt_queue *vq)
{
	u16 old_idx, new_idx, event_idx;

	old_idx		= vq->last_used_signalled;
	new_idx		= vq->vring.used->idx;
	event_idx	= vring_used_event(&vq->vring);

	if (vring_need_event(event_idx, new_idx, old_idx)) {
		vq->last_used_signalled = new_idx;
		return true;
	}

	return false;
}