linux-kernel - [PATCH] xen/balloon: Support xend-based toolstack take two

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Date:   Thu, 16 Jan 2020 18:00:04 +0100
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        stable@...r.kernel.org
Subject: [PATCH] xen/balloon: Support xend-based toolstack take two

Commit 3aa6c19d2f38be ("xen/balloon: Support xend-based toolstack")
tried to fix a regression with running on rather ancient Xen versions.
Unfortunately the fix was based on the assumption that xend would
just use another Xenstore node, but in reality only some downstream
versions of xend are doing that. The upstream xend does not write
that Xenstore node at all, so the problem must be fixed in another
way.

The easiest way to achieve that is to fall back to the behavior before
commit 5266b8e4445c ("xen: fix booting ballooned down hvm guest")
in case the static memory maximum can't be read.

Fixes: 3aa6c19d2f38be ("xen/balloon: Support xend-based toolstack")
Signed-off-by: Juergen Gross <jgross@...e.com>
Cc: <stable@...r.kernel.org> # 4.13
---
 drivers/xen/xen-balloon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
index 6d12fc368210..a8d24433c8e9 100644
--- a/drivers/xen/xen-balloon.c
+++ b/drivers/xen/xen-balloon.c
@@ -94,7 +94,7 @@ static void watch_target(struct xenbus_watch *watch,
 				  "%llu", &static_max) == 1))
 			static_max >>= PAGE_SHIFT - 10;
 		else
-			static_max = new_target;
+			static_max = balloon_stats.current_pages;

 		target_diff = (xen_pv_domain() || xen_initial_domain()) ? 0
 				: static_max - balloon_stats.target_pages;
-- 
2.16.4