Commit be580279 authored by Boqun Feng's avatar Boqun Feng Committed by Wei Liu
Browse files

Drivers: hv: balloon: Disable balloon and hot-add accordingly 



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. This is a
	problem when guest page size > 4096 bytes.

*	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 essential to guest monitoring.
Therefore instead of disabling the entire hv_balloon driver, the
ballooning (when page size > 4096 bytes) and hot-add are disabled
accordingly for now. Once the issues are fixed, they can be re-enable in
these cases.

Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220325023212.1570049-3-boqun.feng@gmail.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
parent b3d6dd09

drivers/hv/hv_balloon.c

+34 −2
Original line number Diff line number Diff line
@@ -1660,6 +1660,38 @@ static void disable_page_reporting(void) 
	}

}



static int ballooning_enabled(void)

{

	/*

	 * Disable ballooning if the page size is not 4k (HV_HYP_PAGE_SIZE),

	 * since currently it's unclear to us whether an unballoon request can

	 * make sure all page ranges are guest page size aligned.

	 */

	if (PAGE_SIZE != HV_HYP_PAGE_SIZE) {

		pr_info("Ballooning disabled because page size is not 4096 bytes\n");

		return 0;

	}



	return 1;

}



static int hot_add_enabled(void)

{

	/*

	 * 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().

	 */

	if (IS_ENABLED(CONFIG_ARM64)) {

		pr_info("Memory hot add disabled on ARM64\n");

		return 0;

	}



	return 1;

}



static int balloon_connect_vsp(struct hv_device *dev)

{

	struct dm_version_request version_req;
@@ -1731,8 +1763,8 @@ static int balloon_connect_vsp(struct hv_device *dev) 
	 * 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.

	 */

	cap_msg.caps.cap_bits.balloon = 1;

	cap_msg.caps.cap_bits.hot_add = 1;

	cap_msg.caps.cap_bits.balloon = ballooning_enabled();

	cap_msg.caps.cap_bits.hot_add = hot_add_enabled();



	/*

	 * Specify our alignment requirements as it relates