From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 15 Jul 2021 07:34:28 +0000 (+0200)
Subject: x86/mem-sharing: ensure consistent lock order in get_two_gfns()
X-Git-Tag: archive/raspbian/4.14.3-1+rpi1^2~44^2~37
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=3cfccd70992b3d2b739e3febfceb99fdf6283be0;p=xen.git

x86/mem-sharing: ensure consistent lock order in get_two_gfns()

While the comment validly says "Sort by domain, if same domain by gfn",
the implementation also included equal domain IDs in the first part of
the check, thus rending the second part entirely dead and leaving
deadlock potential when there's only a single domain involved.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
master commit: 09af2d01a2fe6a0af08598bdfe12c9707f4d82ba
master date: 2021-07-07 12:35:12 +0200
---

diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 8abae345e8..2883d8a2f0 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -552,7 +552,7 @@ do {                                                    \
     dest ## _t   = (source ## t)   ?: &scratch_t;       \
 } while (0)
 
-    if ( (rd->domain_id <= ld->domain_id) ||
+    if ( (rd->domain_id < ld->domain_id) ||
          ((rd == ld) && (gfn_x(rgfn) <= gfn_x(lgfn))) )
     {
         assign_pointers(first, r);