linux-kernel - Re: [PATCH 4/5] KVM: x86: Wrong register masking in 64-bit mode

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Message-ID: <536A56C3.7050907@redhat.com>
Date:	Wed, 07 May 2014 17:52:35 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>, mtosatti@...hat.com,
	hpa@...or.com
CC:	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] KVM: x86: Wrong register masking in 64-bit mode

Il 07/05/2014 14:32, Nadav Amit ha scritto:
> 32-bit operations are zero extended in 64-bit mode. Currently, the code does
> not handle them correctly and keeps the high bits. In 16-bit mode, the high
> 32-bits are kept intact.
>
> 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 (as if an assignment was performed to ECX).

Is this true even for REPZ and ZF=0 or REPNZ and ZF=1?

Paolo
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