Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755244AbaDTJ1F (ORCPT ); Sun, 20 Apr 2014 05:27:05 -0400 Received: from mail-ee0-f47.google.com ([74.125.83.47]:52086 "EHLO mail-ee0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754911AbaDTJ0w (ORCPT ); Sun, 20 Apr 2014 05:26:52 -0400 Date: Sun, 20 Apr 2014 12:26:47 +0300 From: Gleb Natapov To: Nadav Amit Cc: pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/5] KVM: x86: RSI/RDI/RCX are zero-extended when affected by string ops Message-ID: <20140420092646.GB30377@minantech.com> References: <1397777591-6147-1-git-send-email-namit@cs.technion.ac.il> <1397794294-8414-1-git-send-email-namit@cs.technion.ac.il> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1397794294-8414-1-git-send-email-namit@cs.technion.ac.il> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 18, 2014 at 07:11:33AM +0300, Nadav Amit wrote: > When using address-size override prefix with string instructions in long-mode, > ESI/EDI/ECX are zero extended if they are affected by the instruction > (incremented/decremented). Currently, the KVM emulator does not do so. > > In addition, although it is not well-documented, when address override prefix > is used with REP-string instruction, RCX high half is zeroed even if ECX was > zero on the first iteration. Therefore, the emulator should clear the upper > part of RCX in this case, as x86 CPUs do. > > Signed-off-by: Nadav Amit > --- > :100644 100644 69e2636... a69ed67... M arch/x86/kvm/emulate.c > arch/x86/kvm/emulate.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index 69e2636..a69ed67 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -491,6 +491,8 @@ register_address_increment(struct x86_emulate_ctxt *ctxt, unsigned long *reg, in > else > mask = ad_mask(ctxt); > masked_increment(reg, mask, inc); > + if (ctxt->ad_bytes == 4) > + *reg &= 0xffffffff; *reg=(u32)*reg; and you can do it inside else part. register_address_increment() is used also by jmp_rel and loop instructions, is this correct for both of those too? Probably yes. > } > > static void rsp_increment(struct x86_emulate_ctxt *ctxt, int inc) > @@ -4567,6 +4569,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) > if (ctxt->rep_prefix && (ctxt->d & String)) { > /* All REP prefixes have the same first termination condition */ > if (address_mask(ctxt, reg_read(ctxt, VCPU_REGS_RCX)) == 0) { > + if (ctxt->ad_bytes == 4) > + *reg_write(ctxt, VCPU_REGS_RCX) = 0; Does zero extension happens even if ECX was zero at the beginning on an instruction or only during ECX modification. If later it is already covered in register_address_increment, no? > ctxt->eip = ctxt->_eip; > goto done; > } > -- > 1.7.10.4 > -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/