From: Boqun Feng <boqun.feng@xxxxxxxxx> Sent: Wednesday, February 23, 2022 5:16 AM
>
> Currently there are known potential issues for balloon and hot-add on
> ARM64:
>
> * Unballoon requests from Hyper-V should only unballoon ranges
> that are guest page size aligned, otherwise guests cannot handle
> because it's impossible to partially free a page.
>
> * Memory hot-add requests from Hyper-V should provide the NUMA
> node id of the added ranges or ARM64 should have a functional
> memory_add_physaddr_to_nid(), otherwise the node id is missing
> for add_memory().
>
> These issues require discussions on design and implementation. In the
> meanwhile, post_status() is working and essiential to guest monitoring.
> Therefore instead of the entire hv_balloon driver, the balloon and
> hot-add are disabled accordingly for now. Once the issues are fixed,
> they can be re-enable in these cases.
>
> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> ---
> drivers/hv/hv_balloon.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index 062156b88a87..35dcda20be85 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -1730,9 +1730,19 @@ static int balloon_connect_vsp(struct hv_device *dev)
> * When hibernation (i.e. virtual ACPI S4 state) is enabled, the host
> * currently still requires the bits to be set, so we have to add code
> * to fail the host's hot-add and balloon up/down requests, if any.
> + *
> + * We disable balloon if the page size is larger than 4k, since
> + * currently it's unclear to us whether an unballoon request can make
> + * sure all page ranges are guest page size aligned.
> + *
> + * We also disable hot add on ARM64, because we currently rely on
> + * memory_add_physaddr_to_nid() to get a node id of a hot add range,
> + * however ARM64's memory_add_physaddr_to_nid() always return 0 and
> + * DM_MEM_HOT_ADD_REQUEST doesn't have the NUMA node information for
> + * add_memory().
> */
> - cap_msg.caps.cap_bits.balloon = 1;
> - cap_msg.caps.cap_bits.hot_add = 1;
> + cap_msg.caps.cap_bits.balloon = !(PAGE_SIZE > 4096UL);
Any reasons not to use HV_HYP_PAGE_SIZE vs. open coding "4096"? So
cap_msg.caps.cap_bits.balloon = (PAGE_SIZE == HV_HYP_PAGE_SIZE);
> + cap_msg.caps.cap_bits.hot_add = !IS_ENABLED(CONFIG_ARM64);
I think we should output a message so that there's no mystery as to
whether ballooning and/or hot_add are disabled, and why. Each setting
should have its own message. Maybe something like:
if (!cap_msg.caps.cap_bits.balloon)
pr_info("Ballooning disabled because page size is not 4096 bytes\n");
if (!cap_msg.cap_bits.hot_add)
pr_info("Memory hot add disabled on ARM64\n");
>
> /*
> * Specify our alignment requirements as it relates
> --
> 2.35.1
