From 045094933dc7ca7a4a35b2ebd582f6ed226684da Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Fri, 20 Jan 2017 14:36:58 +0100 Subject: [PATCH] x86emul: CMPXCHG{8,16}B are memory writes This fixes a regression introduced by commit ff913f68c9 ("x86/PV: restrict permitted instructions during memory write emulation") breaking namely 32-bit PV guests (which commonly use CMPXCHG8B for certain page table updates). Reported-by: Andrew Cooper Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- xen/arch/x86/x86_emulate/x86_emulate.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index 880d565eb9..520311f930 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -6566,6 +6566,9 @@ x86_insn_is_mem_write(const struct x86_emulate_state *state, case X86EMUL_OPC(0x0f, 0xba): return (state->modrm_reg & 7) > 4; /* BTS / BTR / BTC */ + + case X86EMUL_OPC(0x0f, 0xc7): + return (state->modrm_reg & 7) == 1; /* CMPXCHG{8,16}B */ } return false; -- 2.30.2