aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorRusty Russell <rusty@rustcorp.com.au>2007-11-11 21:39:18 -0500
committerRusty Russell <rusty@rustcorp.com.au>2007-11-11 21:59:40 -0500
commit42b36cc0ce717deeb10030141a43dede763a3ebe (patch)
treeb2dc48b4f16c5dc59461ad24b027d631edda1da4
parent1200e646ae238afc536be70257290eb33fb6e364 (diff)
virtio: Force use of power-of-two for descriptor ring sizes
The virtio descriptor rings of size N-1 were nicely set up to be aligned to an N-byte boundary. But as Anthony Liguori points out, the free-running indices used by virtio require that the sizes be a power of 2, otherwise we get problems on wrap (demonstrated with lguest). So we replace the clever "2^n-1" scheme with a simple "align to page boundary" scheme: this means that all virtio rings take at least two pages, but it's safer than guessing cache alignment. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--Documentation/lguest/lguest.c9
-rw-r--r--drivers/lguest/lguest_device.c3
-rw-r--r--drivers/virtio/virtio_ring.c8
-rw-r--r--include/linux/virtio_ring.h19
4 files changed, 25 insertions, 14 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 157f6a26b939..42008395534d 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -62,8 +62,8 @@ typedef uint8_t u8;
62#endif 62#endif
63/* We can have up to 256 pages for devices. */ 63/* We can have up to 256 pages for devices. */
64#define DEVICE_PAGES 256 64#define DEVICE_PAGES 256
65/* This fits nicely in a single 4096-byte page. */ 65/* This will occupy 2 pages: it must be a power of 2. */
66#define VIRTQUEUE_NUM 127 66#define VIRTQUEUE_NUM 128
67 67
68/*L:120 verbose is both a global flag and a macro. The C preprocessor allows 68/*L:120 verbose is both a global flag and a macro. The C preprocessor allows
69 * this, and although I wouldn't recommend it, it works quite nicely here. */ 69 * this, and although I wouldn't recommend it, it works quite nicely here. */
@@ -1036,7 +1036,8 @@ static void add_virtqueue(struct device *dev, unsigned int num_descs,
1036 void *p; 1036 void *p;
1037 1037
1038 /* First we need some pages for this virtqueue. */ 1038 /* First we need some pages for this virtqueue. */
1039 pages = (vring_size(num_descs) + getpagesize() - 1) / getpagesize(); 1039 pages = (vring_size(num_descs, getpagesize()) + getpagesize() - 1)
1040 / getpagesize();
1040 p = get_pages(pages); 1041 p = get_pages(pages);
1041 1042
1042 /* Initialize the configuration. */ 1043 /* Initialize the configuration. */
@@ -1045,7 +1046,7 @@ static void add_virtqueue(struct device *dev, unsigned int num_descs,
1045 vq->config.pfn = to_guest_phys(p) / getpagesize(); 1046 vq->config.pfn = to_guest_phys(p) / getpagesize();
1046 1047
1047 /* Initialize the vring. */ 1048 /* Initialize the vring. */
1048 vring_init(&vq->vring, num_descs, p); 1049 vring_init(&vq->vring, num_descs, p, getpagesize());
1049 1050
1050 /* Add the configuration information to this device's descriptor. */ 1051 /* Add the configuration information to this device's descriptor. */
1051 add_desc_field(dev, VIRTIO_CONFIG_F_VIRTQUEUE, 1052 add_desc_field(dev, VIRTIO_CONFIG_F_VIRTQUEUE,
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 8904f72f97c6..66f38722253a 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -200,7 +200,8 @@ static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
200 200
201 /* Figure out how many pages the ring will take, and map that memory */ 201 /* Figure out how many pages the ring will take, and map that memory */
202 lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT, 202 lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
203 DIV_ROUND_UP(vring_size(lvq->config.num), 203 DIV_ROUND_UP(vring_size(lvq->config.num,
204 PAGE_SIZE),
204 PAGE_SIZE)); 205 PAGE_SIZE));
205 if (!lvq->pages) { 206 if (!lvq->pages) {
206 err = -ENOMEM; 207 err = -ENOMEM;
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 0e1bf053d8cd..1dc04b6684e6 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -277,11 +277,17 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
277 struct vring_virtqueue *vq; 277 struct vring_virtqueue *vq;
278 unsigned int i; 278 unsigned int i;
279 279
280 /* We assume num is a power of 2. */
281 if (num & (num - 1)) {
282 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
283 return NULL;
284 }
285
280 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL); 286 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
281 if (!vq) 287 if (!vq)
282 return NULL; 288 return NULL;
283 289
284 vring_init(&vq->vring, num, pages); 290 vring_init(&vq->vring, num, pages, PAGE_SIZE);
285 vq->vq.callback = callback; 291 vq->vq.callback = callback;
286 vq->vq.vdev = vdev; 292 vq->vq.vdev = vdev;
287 vq->vq.vq_ops = &vring_vq_ops; 293 vq->vq.vq_ops = &vring_vq_ops;
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 5b88d215af50..1a4ed49f6478 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -67,7 +67,7 @@ struct vring {
67}; 67};
68 68
69/* The standard layout for the ring is a continuous chunk of memory which looks 69/* The standard layout for the ring is a continuous chunk of memory which looks
70 * like this. The used fields will be aligned to a "num+1" boundary. 70 * like this. We assume num is a power of 2.
71 * 71 *
72 * struct vring 72 * struct vring
73 * { 73 * {
@@ -79,8 +79,8 @@ struct vring {
79 * __u16 avail_idx; 79 * __u16 avail_idx;
80 * __u16 available[num]; 80 * __u16 available[num];
81 * 81 *
82 * // Padding so a correctly-chosen num value will cache-align used_idx. 82 * // Padding to the next page boundary.
83 * char pad[sizeof(struct vring_desc) - sizeof(avail_flags)]; 83 * char pad[];
84 * 84 *
85 * // A ring of used descriptor heads with free-running index. 85 * // A ring of used descriptor heads with free-running index.
86 * __u16 used_flags; 86 * __u16 used_flags;
@@ -88,18 +88,21 @@ struct vring {
88 * struct vring_used_elem used[num]; 88 * struct vring_used_elem used[num];
89 * }; 89 * };
90 */ 90 */
91static inline void vring_init(struct vring *vr, unsigned int num, void *p) 91static inline void vring_init(struct vring *vr, unsigned int num, void *p,
92 unsigned int pagesize)
92{ 93{
93 vr->num = num; 94 vr->num = num;
94 vr->desc = p; 95 vr->desc = p;
95 vr->avail = p + num*sizeof(struct vring_desc); 96 vr->avail = p + num*sizeof(struct vring_desc);
96 vr->used = p + (num+1)*(sizeof(struct vring_desc) + sizeof(__u16)); 97 vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + pagesize-1)
98 & ~(pagesize - 1));
97} 99}
98 100
99static inline unsigned vring_size(unsigned int num) 101static inline unsigned vring_size(unsigned int num, unsigned int pagesize)
100{ 102{
101 return (num + 1) * (sizeof(struct vring_desc) + sizeof(__u16)) 103 return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
102 + sizeof(__u32) + num * sizeof(struct vring_used_elem); 104 + pagesize - 1) & ~(pagesize - 1))
105 + sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
103} 106}
104 107
105#ifdef __KERNEL__ 108#ifdef __KERNEL__