On Fri, Feb 25, 2022 at 05:06:45PM +0000, Michael Kelley (LINUX) wrote:
> From: Boqun Feng <boqun.feng@xxxxxxxxx> Sent: Thursday, February 24, 2022 6:17 PM
> >
> > 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.
>
> The above problem occurs only when the guest page size is > 4 Kbytes.
>
Ok, I wil call it out in next version.
> >
> > * 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.
>
> s/essiential/essential/
>
> > 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.
>
> Missing the word "disabling" in the first line? Also the balloon
The phrasing that I was trying to use here is "Instead of A, B and C are
disabled" or "B and C are disabled instead of A". Looks like I'm
inventing my own English? Any I will add the "disabling" in the next
version ;-)
Regards,
Boqun
> function is disabled only if the page size is > 4 Kbytes.
>
> >
> > Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> > ---
> > v1 --> v1.1:
> >
> > * Use HV_HYP_PAGE_SIZE instead of hard coding 4096 as suggested by
> > Michael.
> >
> > * Explicitly print out the disable message if a function is
> > disabled as suggested by Michael.
> >
> > drivers/hv/hv_balloon.c | 36 ++++++++++++++++++++++++++++++++++--
> > 1 file changed, 34 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> > index 062156b88a87..eee7402cfc02 100644
> > --- a/drivers/hv/hv_balloon.c
> > +++ b/drivers/hv/hv_balloon.c
> > @@ -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.
>
> My interpretation of the conversations with Hyper-V is that that they clearly
> don't guarantee page ranges are guest page 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
> > --
> > 2.33.0
>
> The code looks good to me.
>
> Michael
