Re: [regression] Bug 221745 - PV DomU ballooning driver init issue

Hello

It works !!!

uname -a
Linux status 7.2.0-rc3-xendomu #1 SMP PREEMPT Thu Jul 30 10:39:13 CEST 
2026 x86_64 GNU/Linux

# ps auxwwwf | grep -i ball
root          48  0.0  0.0      0     0 ?        S    11:33   0:00 \_ 
[xen-balloon]

dmesg  | grep -i ballo
[    0.436657] xen:balloon: Initialising balloon driver

domU memory resize works, tested 1024m -> 1200m -> 1000m.

Regards


Le 27/07/2026 à 19:10, Yannick Martin a écrit :
> Hello
>
> I will try this tomorrow !
>
> Regards
>
>
> Le 27 juillet 2026 18:51:15 GMT+02:00, "Roger Pau Monné" 
> <[email protected]> a écrit :
>
>     On Mon, Jul 27, 2026 at 10:42:25AM +0200, Thorsten Leemhuis wrote:
>
>         Hi Roger! FYI, it seems your change 0949c646d64697 ("Partial
>         revert "x86/xen: fix balloon target initialization for PVH
>         dom0"") [v7.0-rc1] caued a regression. For details see
>         https://bugzilla.kernel.org/show_bug.cgi?id=221745 To quote
>         the initial comment:
>
>             Since commit db8c4b1 (Partial revert "x86/xen: fix balloon
>             target initialization for PVH dom0"), xen ballooning fails
>             to init correctly on domU (on amd64 arch) with the
>             following configuration: -- xl.cfg ... memory = '2048'
>             maxmem = '4096' ... -- -- domU balloon dmesg (init fails)
>             [ 0.908337] xen:balloon: Initialising balloon driver [
>             0.940721] Extra pages underflow current target 
>
>     Yeah, I'm afraid the original fix commit didn't fully fix the
>     issues, so there's the following change (chunk below) that's
>     needed additionally to cope with memory != maxmem on PV guests.
>     I've done some basic testing and it seems to solve the issue,
>     could you give it a spin also? (just to make sure I'm not missing
>     anything else). Thanks, Roger.
>     ------------------------------------------------------------------------
>     diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index
>     e7f1d4ca6d75..c20a1ff8292d 100644 --- a/drivers/xen/balloon.c +++
>     b/drivers/xen/balloon.c @@ -703,19 +703,26 @@ static int __init
>     balloon_add_regions(void) balloon_append(pfn_to_page(pfn)); /* - *
>     Extra regions are accounted for in the physmap, but need - *
>     decreasing from current_pages and target_pages to balloon - * down
>     the initial allocation, because they are already - * accounted for
>     in total_pages. + * For HVM domains: extra regions are accounted
>     for in the + * physmap, but need decreasing from current_pages and
>     + * target_pages to balloon down the initial allocation, because +
>     * they are already accounted for in total_pages. + * + * For PV
>     domains: extra regions are not accounted for in the + * initial
>     memory target, and hence need adding to the stats as + *
>     additional unpopulated regions. */ pages = extra_pfn_end -
>     start_pfn; - if (pages >= balloon_stats.current_pages || - pages
>     >= balloon_stats.target_pages) { + if (xen_pv_domain()) { +
>     balloon_stats.total_pages += pages; + } else if (pages >=
>     balloon_stats.current_pages || + pages >=
>     balloon_stats.target_pages) { WARN(1, "Extra pages underflow
>     current target"); return -ERANGE; + } else { +
>     balloon_stats.current_pages -= pages; + balloon_stats.target_pages
>     -= pages; } - balloon_stats.current_pages -= pages; -
>     balloon_stats.target_pages -= pages; } return 0;
>