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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 /drivers/lguest
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>
Diffstat (limited to 'drivers/lguest')
-rw-r--r--drivers/lguest/lguest_device.c3
1 files changed, 2 insertions, 1 deletions
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;