[xen stable-4.13] x86/mem-sharing: ensure consistent lock order in get_two_gfns()

[patchbot@xxxxxxx]

commit 1540a9a20dd0c049345a00bfed0a3e8ea98d104b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jul 15 09:44:20 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 15 09:44:20 2021 +0200

    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@xxxxxxxx>
    Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
    master commit: 09af2d01a2fe6a0af08598bdfe12c9707f4d82ba
    master date: 2021-07-07 12:35:12 +0200
---
 xen/include/asm-x86/p2m.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 94285db1b4..2358954039 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -556,7 +556,7 @@ 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);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.13