From 2fcf5c8ae244b4c298d2111a288d410a719ac626 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Mon, 26 Jan 2015 09:32:21 +0200 Subject: [PATCH] KVM: x86: Dirty the dest op page on cmpxchg emulation MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Intel SDM says for CMPXCHG: "To simplify the interface to the processor’s bus, the destination operand receives a write cycle without regard to the result of the comparison.". This means the destination page should be dirtied. Fix it to by writing back the original value if cmpxchg failed. Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index ef23c1e5fa9f..aa272545402e 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -2205,12 +2205,15 @@ static int em_cmpxchg(struct x86_emulate_ctxt *ctxt) fastop(ctxt, em_cmp); if (ctxt->eflags & EFLG_ZF) { - /* Success: write back to memory. */ + /* Success: write back to memory; no update of EAX */ + ctxt->src.type = OP_NONE; ctxt->dst.val = ctxt->src.orig_val; } else { /* Failure: write the value we saw to EAX. */ - ctxt->dst.type = OP_REG; - ctxt->dst.addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX); + ctxt->src.type = OP_REG; + ctxt->src.addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX); + ctxt->src.val = ctxt->dst.orig_val; + /* Create write-cycle to dest by writing the same value */ ctxt->dst.val = ctxt->dst.orig_val; } return X86EMUL_CONTINUE; @@ -4157,7 +4160,7 @@ static const struct opcode twobyte_table[256] = { F(DstMem | SrcReg | Src2CL | ModRM, em_shrd), GD(0, &group15), F(DstReg | SrcMem | ModRM, em_imul), /* 0xB0 - 0xB7 */ - I2bv(DstMem | SrcReg | ModRM | Lock | PageTable, em_cmpxchg), + I2bv(DstMem | SrcReg | ModRM | Lock | PageTable | SrcWrite, em_cmpxchg), I(DstReg | SrcMemFAddr | ModRM | Src2SS, em_lseg), F(DstMem | SrcReg | ModRM | BitOp | Lock, em_btr), I(DstReg | SrcMemFAddr | ModRM | Src2FS, em_lseg), -- 2.45.2