virtio: avoid implicit use of Linux page size in balloon interface Date: Thu, 13 Nov 2008 15:48:33 -0600 From: Hollis Blanchard Make the balloon interface always use 4K pages, and convert Linux pfns if necessary. This patch assumes that Linux's PAGE_SHIFT will never be less than 12. Signed-off-by: Hollis Blanchard Signed-off-by: Rusty Russell --- drivers/virtio/virtio_balloon.c | 12 ++++++++++-- include/linux/virtio_balloon.h | 3 +++ 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -56,6 +56,14 @@ static struct virtio_device_id id_table[ { 0 }, }; +static u32 page_to_balloon_pfn(struct page *page) +{ + unsigned long pfn = page_to_pfn(page); + + /* Convert pfn from Linux page size to balloon page size. */ + return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT); +} + static void balloon_ack(struct virtqueue *vq) { struct virtio_balloon *vb; @@ -99,7 +107,7 @@ static void fill_balloon(struct virtio_b msleep(200); break; } - vb->pfns[vb->num_pfns] = page_to_pfn(page); + vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page); totalram_pages--; vb->num_pages++; list_add(&page->lru, &vb->pages); @@ -132,7 +140,7 @@ static void leak_balloon(struct virtio_b for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) { page = list_first_entry(&vb->pages, struct page, lru); list_del(&page->lru); - vb->pfns[vb->num_pfns] = page_to_pfn(page); + vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page); vb->num_pages--; } diff --git a/include/linux/virtio_balloon.h b/include/linux/virtio_balloon.h --- a/include/linux/virtio_balloon.h +++ b/include/linux/virtio_balloon.h @@ -10,6 +10,9 @@ /* The feature bitmap for virtio balloon */ #define VIRTIO_BALLOON_F_MUST_TELL_HOST 0 /* Tell before reclaiming pages */ +/* Size of a PFN in the balloon interface. */ +#define VIRTIO_BALLOON_PFN_SHIFT 12 + struct virtio_balloon_config { /* Number of pages host wants Guest to give up. */