// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2016 Red Hat, Inc.
* Author: Michael S. Tsirkin <[email protected]>
*
* Partial implementation of virtio 0.9. event index is used for signalling,
* unconditionally. Design roughly follows linux kernel implementation in order
* to be able to judge its performance.
*/
#define _GNU_SOURCE
#include "main.h"
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <linux/virtio_ring.h>
struct data {
void *data;
} *data;
struct vring ring;
/* enabling the below activates experimental ring polling code
* (which skips index reads on consumer in favor of looking at
* high bits of ring id ^ 0x8000).
*/
/* #ifdef RING_POLL */
/* enabling the below activates experimental in-order code
* (which skips ring updates and reads and writes len in descriptor).
*/
/* #ifdef INORDER */
#if defined(RING_POLL) && defined(INORDER)
#error "RING_POLL and INORDER are mutually exclusive"
#endif
/* how much padding is needed to avoid false cache sharing */
#define HOST_GUEST_PADDING 0x80
struct guest {
unsigned short avail_idx;
unsigned short last_used_idx;
unsigned short num_free;
unsigned short kicked_avail_idx;
#ifndef INORDER
unsigned short free_head;
#else
unsigned short reserved_free_head;
#endif
unsigned char reserved[HOST_GUEST_PADDING - 10];
} guest;
struct host {
/* we do not need to track last avail index
* unless we have more than one in flight.
*/
unsigned short used_idx;
unsigned short called_used_idx;
unsigned char reserved[HOST_GUEST_PADDING - 4];
} host;
/* implemented by ring */
void alloc_ring(void)
{
int ret;
int i;
void *p;
ret = posix_memalign(&p, 0x1000, vring_size(ring_size, 0x1000));
if (ret) {
perror("Unable to allocate ring buffer.\n");
exit(3);
}
memset(p, 0, vring_size(ring_size, 0x1000));
vring_init(&ring, ring_size, p, 0x1000);
guest.avail_idx = 0;
guest.kicked_avail_idx = -1;
guest.last_used_idx = 0;
#ifndef INORDER
/* Put everything in free lists. */
guest.free_head = 0;
#endif
for (i = 0; i < ring_size - 1; i++)
ring.desc[i].next = i + 1;
host.used_idx = 0;
host.called_used_idx = -1;
guest.num_free = ring_size;
data = malloc(ring_size * sizeof *data);
if (!data) {
perror("Unable to allocate data buffer.\n");
exit(3);
}
memset(data, 0, ring_size * sizeof *data);
}
/* guest side */
int add_inbuf(unsigned len, void *buf, void *datap)
{
unsigned head;
#ifndef INORDER
unsigned avail;
#endif
struct vring_desc *desc;
if (!guest.num_free)
return -1;
#ifdef INORDER
head = (ring_size - 1) & (guest.avail_idx++);
#else
head = guest.free_head;
#endif
guest.num_free--;
desc = ring.desc;
desc[head].flags = VRING_DESC_F_NEXT;
desc[head].addr = (unsigned long)(void *)buf;
desc[head].len = len;
/* We do it like this to simulate the way
* we'd have to flip it if we had multiple
* descriptors.
*/
desc[head].flags &= ~VRING_DESC_F_NEXT;
#ifndef INORDER
guest.free_head = desc[head].next;
#endif
data[head].data = datap;
#ifdef RING_POLL
/* Barrier A (for pairing) */
smp_release();
avail = guest.avail_idx++;
ring.avail->ring[avail & (ring_size - 1)] =
(head | (avail & ~(ring_size - 1))) ^ 0x8000;
#else
#ifndef INORDER
/* Barrier A (for pairing) */
smp_release();
avail = (ring_size - 1) & (guest.avail_idx++);
ring.avail->ring[avail] = head;
#endif
/* Barrier A (for pairing) */
smp_release();
#endif
ring.avail->idx = guest.avail_idx;
return 0;
}
void *get_buf(unsigned *lenp, void **bufp)
{
unsigned head;
unsigned index;
void *datap;
#ifdef RING_POLL
head = (ring_size - 1) & guest.last_used_idx;
index = ring.used->ring[head].id;
if ((index ^ guest.last_used_idx ^ 0x8000) & ~(ring_size - 1))
return NULL;
/* Barrier B (for pairing) */
smp_acquire();
index &= ring_size - 1;
#else
if (ring.used->idx == guest.last_used_idx)
return NULL;
/* Barrier B (for pairing) */
smp_acquire();
#ifdef INORDER
head = (ring_size - 1) & guest.last_used_idx;
index = head;
#else
head = (ring_size - 1) & guest.last_used_idx;
index = ring.used->ring[head].id;
#endif
#endif
#ifdef INORDER
*lenp = ring.desc[index].len;
#else
*lenp = ring.used->ring[head].len;
#endif
datap = data[index].data;
*bufp = (void*)(unsigned long)ring.desc[index].addr;
data[index].data = NULL;
#ifndef INORDER
ring.desc[index].next = guest.free_head;
guest.free_head = index;
#endif
guest.num_free++;
guest.last_used_idx++;
return datap;
}
bool used_empty()
{
unsigned short last_used_idx = guest.last_used_idx;
#ifdef RING_POLL
unsigned short head = last_used_idx & (ring_size - 1);
unsigned index = ring.used->ring[head].id;
return (index ^ last_used_idx ^ 0x8000) & ~(ring_size - 1);
#else
return ring.used->idx == last_used_idx;
#endif
}
void disable_call()
{
/* Doing nothing to disable calls might cause
* extra interrupts, but reduces the number of cache misses.
*/
}
bool enable_call()
{
vring_used_event(&ring) = guest.last_used_idx;
/* Flush call index write */
/* Barrier D (for pairing) */
smp_mb();
return used_empty();
}
void kick_available(void)
{
bool need;
/* Flush in previous flags write */
/* Barrier C (for pairing) */
smp_mb();
need = vring_need_event(vring_avail_event(&ring),
guest.avail_idx,
guest.kicked_avail_idx);
guest.kicked_avail_idx = guest.avail_idx;
if (need)
kick();
}
/* host side */
void disable_kick()
{
/* Doing nothing to disable kicks might cause
* extra interrupts, but reduces the number of cache misses.
*/
}
bool enable_kick()
{
vring_avail_event(&ring) = host.used_idx;
/* Barrier C (for pairing) */
smp_mb();
return avail_empty();
}
bool avail_empty()
{
unsigned head = host.used_idx;
#ifdef RING_POLL
unsigned index = ring.avail->ring[head & (ring_size - 1)];
return ((index ^ head ^ 0x8000) & ~(ring_size - 1));
#else
return head == ring.avail->idx;
#endif
}
bool use_buf(unsigned *lenp, void **bufp)
{
unsigned used_idx = host.used_idx;
struct vring_desc *desc;
unsigned head;
#ifdef RING_POLL
head = ring.avail->ring[used_idx & (ring_size - 1)];
if ((used_idx ^ head ^ 0x8000) & ~(ring_size - 1))
return false;
/* Barrier A (for pairing) */
smp_acquire();
used_idx &= ring_size - 1;
desc = &ring.desc[head & (ring_size - 1)];
#else
if (used_idx == ring.avail->idx)
return false;
/* Barrier A (for pairing) */
smp_acquire();
used_idx &= ring_size - 1;
#ifdef INORDER
head = used_idx;
#else
head = ring.avail->ring[used_idx];
#endif
desc = &ring.desc[head];
#endif
*lenp = desc->len;
*bufp = (void *)(unsigned long)desc->addr;
#ifdef INORDER
desc->len = desc->len - 1;
#else
/* now update used ring */
ring.used->ring[used_idx].id = head;
ring.used->ring[used_idx].len = desc->len - 1;
#endif
/* Barrier B (for pairing) */
smp_release();
host.used_idx++;
ring.used->idx = host.used_idx;
return true;
}
void call_used(void)
{
bool need;
/* Flush in previous flags write */
/* Barrier D (for pairing) */
smp_mb();
need = vring_need_event(vring_used_event(&ring),
host.used_idx,
host.called_used_idx);
host.called_used_idx = host.used_idx;
if (need)
call();
}
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