From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> Sent: Thursday, January 16, 2020 6:16 AM
>
> 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;
The above test is no longer necessary. The num_pages < alloc_unit
case is handled implicitly by your new 'for' loop condition.
>
> - 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) {
Maybe I'm missing something, but I don't think Vitaly's optimization works. If
alloc_unit specifies 2 Mbytes, and num_pages specifies 3 Mbytes, then num_ballooned
will come back as 2 Mbytes, which is correct. But if we revert alloc_unit to 1 page and
"continue" in that case, we will lose the 2 Mbytes of memory (it's not freed), and the
next time through the loop will try to allocate only 1 Mbyte (because num_pages
will be decremented by num_ballooned). I think the original code does the right thing.
Michael
> alloc_unit = 1;
> continue;
> }
> --
> 2.14.5
