[Xen-devel] [PATCH v3 2/3] xen: actually skip the first MAX_ORDER bits in pfn_pdx_hole_setup

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

pfn_pdx_hole_setup is meant to skip the first MAX_ORDER bits, but
actually it only skips the first MAX_ORDER-1 bits. The issue was
probably introduced by bdb5439c3f ("x86_64: Ensure frame-table
compression leaves MAX_ORDER aligned"), when changing to loop to start
from MAX_ORDER-1 an adjustment by 1 was needed in the call to
find_next_bit() but not done.

Fix the issue by passing j+1 and i+1 to find_next_zero_bit and
find_next_bit. Also add a check for i >= BITS_PER_LONG because
find_{,next_}zero_bit() are free to assume that their last argument is
less than their middle one.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
Signed-off-by: Jan Beulich <JBeulich@xxxxxxxx>
CC: andrew.cooper3@xxxxxxxxxx
CC: JBeulich@xxxxxxxx
CC: George.Dunlap@xxxxxxxxxxxxx
CC: ian.jackson@xxxxxxxxxxxxx
CC: konrad.wilk@xxxxxxxxxx
CC: tim@xxxxxxx
CC: wei.liu2@xxxxxxxxxx
---
Changes in v2:
- add commit title of bdb5439c3f
- more CC
- update commit message
---
 xen/common/pdx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index 50c21b6bf8..bb7e437049 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -83,8 +83,10 @@ void __init pfn_pdx_hole_setup(unsigned long mask)
      */
     for ( j = MAX_ORDER-1; ; )
     {
-        i = find_next_zero_bit(&mask, BITS_PER_LONG, j);
-        j = find_next_bit(&mask, BITS_PER_LONG, i);
+        i = find_next_zero_bit(&mask, BITS_PER_LONG, j + 1);
+        if ( i >= BITS_PER_LONG )
+            break;
+        j = find_next_bit(&mask, BITS_PER_LONG, i + 1);
         if ( j >= BITS_PER_LONG )
             break;
         if ( j - i > hole_shift )
-- 
2.17.1


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