From: Roger Pau Monne Date: Wed, 14 May 2025 08:04:26 +0000 (+0200) Subject: xen/x86: fix initial memory balloon target X-Git-Tag: v6.16-rc1~158^2~1 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=74287971dbb3fe322bb316afd9e7fb5807e23bee;p=thirdparty%2Fkernel%2Flinux.git xen/x86: fix initial memory balloon target When adding extra memory regions as ballooned pages also adjust the balloon target, otherwise when the balloon driver is started it will populate memory to match the target value and consume all the extra memory regions added. This made the usage of the Xen `dom0_mem=,max:` command line parameter for dom0 not work as expected, as the target won't be adjusted and when the balloon is started it will populate memory straight to the 'max:' value. It would equally affect domUs that have memory != maxmem. Kernels built with CONFIG_XEN_UNPOPULATED_ALLOC are not affected, because the extra memory regions are consumed by the unpopulated allocation driver, and then balloon_add_regions() becomes a no-op. Reported-by: John Fixes: 87af633689ce ('x86/xen: fix balloon target initialization for PVH dom0') Signed-off-by: Roger Pau Monné Reviewed-by: Juergen Gross Tested-by: Marek Marczykowski-Górecki Message-ID: <20250514080427.28129-1-roger.pau@citrix.com> Signed-off-by: Juergen Gross --- diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 8c852807ba1c1..2de37dcd75566 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -704,15 +704,18 @@ static int __init balloon_add_regions(void) /* * Extra regions are accounted for in the physmap, but need - * decreasing from current_pages to balloon down the initial - * allocation, because they are already accounted for in - * total_pages. + * decreasing from current_pages and target_pages to balloon + * down the initial allocation, because they are already + * accounted for in total_pages. */ - if (extra_pfn_end - start_pfn >= balloon_stats.current_pages) { + pages = extra_pfn_end - start_pfn; + if (pages >= balloon_stats.current_pages || + pages >= balloon_stats.target_pages) { WARN(1, "Extra pages underflow current target"); return -ERANGE; } - balloon_stats.current_pages -= extra_pfn_end - start_pfn; + balloon_stats.current_pages -= pages; + balloon_stats.target_pages -= pages; } return 0;