From 42b36cc0ce717deeb10030141a43dede763a3ebe Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Mon, 12 Nov 2007 13:39:18 +1100 Subject: 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 --- drivers/lguest/lguest_device.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'drivers/lguest/lguest_device.c') diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c index 8904f72f97c..66f38722253 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, /* Figure out how many pages the ring will take, and map that memory */ lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT, - DIV_ROUND_UP(vring_size(lvq->config.num), + DIV_ROUND_UP(vring_size(lvq->config.num, + PAGE_SIZE), PAGE_SIZE)); if (!lvq->pages) { err = -ENOMEM; -- cgit v1.2.3