[PATCH V1 14/16] xen/ioreq: Use guest_cmpxchg64() instead of cmpxchg()

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

The cmpxchg() in hvm_send_buffered_ioreq() operates on memory shared
with the emulator. In order to be on the safe side we need to switch
to guest_cmpxchg64() to prevent a domain to DoS Xen on Arm.

CC: Julien Grall <jgrall@xxxxxxxxxx>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

---
Please note, this patch depends on the following patch on a review:
https://patchwork.kernel.org/patch/11715559/

Changes RFC -> V1:
   - new patch
---
---
 xen/common/ioreq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
index e24a481..645d8a1 100644
--- a/xen/common/ioreq.c
+++ b/xen/common/ioreq.c
@@ -30,6 +30,8 @@
 #include <xen/trace.h>
 #include <xen/vpci.h>
 
+#include <asm/guest_atomics.h>
+
 #include <public/hvm/dm_op.h>
 #include <public/hvm/ioreq.h>
 #include <public/hvm/params.h>
@@ -1325,7 +1327,7 @@ static int hvm_send_buffered_ioreq(struct 
hvm_ioreq_server *s, ioreq_t *p)
 
         new.read_pointer = old.read_pointer - n * IOREQ_BUFFER_SLOT_NUM;
         new.write_pointer = old.write_pointer - n * IOREQ_BUFFER_SLOT_NUM;
-        cmpxchg(&pg->ptrs.full, old.full, new.full);
+        guest_cmpxchg64(d, &pg->ptrs.full, old.full, new.full);
     }
 
     notify_via_xen_event_channel(d, s->bufioreq_evtchn);
-- 
2.7.4