[RFC PATCH v1 35/57] virtio: Remove PAGE_SIZE compile-time constant assumption

Ryan Roberts
2024-10-14T12:13:16Z

To prepare for supporting boot-time page size selection, refactor code
to remove assumptions about PAGE_SIZE being compile-time constant. Code
intended to be equivalent when compile-time page size is active.

Updated multiple BUILD_BUG_ON() instances to test against page size
limits.

Wrap global variables that are initialized with PAGE_SIZE derived values
using DEFINE_GLOBAL_PAGE_SIZE_VAR() so their initialization can be
deferred for boot-time page size builds.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---

***NOTE***
Any confused maintainers may want to read the cover note here for context:
https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/

drivers/block/virtio_blk.c | 2 +-
drivers/virtio/virtio_balloon.c | 10 ++++++----
net/9p/trans_virtio.c | 4 ++--
3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 194417abc1053..8a8960b609bc9 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -899,7 +899,7 @@ static ssize_t serial_show(struct device *dev,
int err;

/* sysfs gives us a PAGE_SIZE buffer */
- BUILD_BUG_ON(PAGE_SIZE < VIRTIO_BLK_ID_BYTES);
+ BUILD_BUG_ON(PAGE_SIZE_MIN < VIRTIO_BLK_ID_BYTES);

buf[VIRTIO_BLK_ID_BYTES] = '\0';
err = virtblk_get_id(disk, buf);
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 54469277ca303..3818d894bd212 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -25,6 +25,7 @@
* page units.
*/
#define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned int)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
+#define VIRTIO_BALLOON_PAGES_PER_PAGE_MAX (unsigned int)(PAGE_SIZE_MAX >> VIRTIO_BALLOON_PFN_SHIFT)
#define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
/* Maximum number of (4k) pages to deflate on OOM notifications. */
#define VIRTIO_BALLOON_OOM_NR_PAGES 256
@@ -138,7 +139,7 @@ static u32 page_to_balloon_pfn(struct page *page)
{
unsigned long pfn = page_to_pfn(page);

- BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
+ BUILD_BUG_ON(PAGE_SHIFT_MIN < VIRTIO_BALLOON_PFN_SHIFT);
/* Convert pfn from Linux page size to balloon page size. */
return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
}
@@ -228,7 +229,7 @@ static void set_page_pfns(struct virtio_balloon *vb,
{
unsigned int i;

- BUILD_BUG_ON(VIRTIO_BALLOON_PAGES_PER_PAGE > VIRTIO_BALLOON_ARRAY_PFNS_MAX);
+ BUILD_BUG_ON(VIRTIO_BALLOON_PAGES_PER_PAGE_MAX > VIRTIO_BALLOON_ARRAY_PFNS_MAX);

/*
* Set balloon pfns pointing at this page.
@@ -1042,8 +1043,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
* host's base page size. However, it needs more work to report
* that value. The hard-coded order would be fine currently.
*/
-#if defined(CONFIG_ARM64) && defined(CONFIG_ARM64_64K_PAGES)
- vb->pr_dev_info.order = 5;
+#if defined(CONFIG_ARM64)
+ if (PAGE_SIZE == SZ_64K)
+ vb->pr_dev_info.order = 5;
#endif

err = page_reporting_register(&vb->pr_dev_info);
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 0b8086f58ad55..25b8253011cec 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -786,7 +786,7 @@ static struct virtio_driver p9_virtio_drv = {
.remove = p9_virtio_remove,
};

-static struct p9_trans_module p9_virtio_trans = {
+static DEFINE_GLOBAL_PAGE_SIZE_VAR(struct p9_trans_module, p9_virtio_trans, {
.name = "virtio",
.create = p9_virtio_create,
.close = p9_virtio_close,
@@ -804,7 +804,7 @@ static struct p9_trans_module p9_virtio_trans = {
.pooled_rbuffers = false,
.def = 1,
.owner = THIS_MODULE,
-};
+});

/* The standard init function */
static int __init p9_virtio_init(void)
--
2.43.0