[PATCH V2] x86/Hyper-V: Balloon up according to request page number

[lantianyu1986]

From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>

Current code has assumption that balloon request memory size aligns
with 2MB. But actually Hyper-V doesn't guarantee such alignment. When
balloon driver receives non-aligned balloon request, it produces warning
and balloon up more memory than requested in order to keep 2MB alignment.
Remove the warning and balloon up memory according to actual requested
memory size.

Fixes: f6712238471a ("hv: hv_balloon: avoid memory leak on alloc_error of 2MB memory block")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
---
Change since v2:
    - Change logic of switching alloc_unit from 2MB to 4KB
    in the balloon_up() to avoid redundant iteration when
    handle non-aligned page request.
    - Remove 2MB alignment operation and comment in balloon_up()
---
 drivers/hv/hv_balloon.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 7f3e7ab22d5d..536807efbc35 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1684,7 +1684,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
 	if (num_pages < alloc_unit)
 		return 0;
 
-	for (i = 0; (i * alloc_unit) < num_pages; i++) {
+	for (i = 0; i < num_pages / alloc_unit; i++) {
 		if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) >
 			HV_HYP_PAGE_SIZE)
 			return i * alloc_unit;
@@ -1722,7 +1722,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
 
 	}
 
-	return num_pages;
+	return i * alloc_unit;
 }
 
 static void balloon_up(union dm_msg_info *msg_info)
@@ -1737,9 +1737,6 @@ static void balloon_up(union dm_msg_info *msg_info)
 	long avail_pages;
 	unsigned long floor;
 
-	/* The host balloons pages in 2M granularity. */
-	WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0);
-
 	/*
 	 * We will attempt 2M allocations. However, if we fail to
 	 * allocate 2M chunks, we will go back to PAGE_SIZE allocations.
@@ -1749,14 +1746,13 @@ static void balloon_up(union dm_msg_info *msg_info)
 	avail_pages = si_mem_available();
 	floor = compute_balloon_floor();
 
-	/* Refuse to balloon below the floor, keep the 2M granularity. */
+	/* Refuse to balloon below the floor. */
 	if (avail_pages < num_pages || avail_pages - num_pages < floor) {
 		pr_warn("Balloon request will be partially fulfilled. %s\n",
 			avail_pages < num_pages ? "Not enough memory." :
 			"Balloon floor reached.");
 
 		num_pages = avail_pages > floor ? (avail_pages - floor) : 0;
-		num_pages -= num_pages % PAGES_IN_2M;
 	}
 
 	while (!done) {
@@ -1770,7 +1766,7 @@ static void balloon_up(union dm_msg_info *msg_info)
 		num_ballooned = alloc_balloon_pages(&dm_device, num_pages,
 						    bl_resp, alloc_unit);
 
-		if (alloc_unit != 1 && num_ballooned == 0) {
+		if (alloc_unit != 1 && num_ballooned != num_pages) {
 			alloc_unit = 1;
 			continue;
 		}
-- 
2.14.5