linux-kernel - Re: [PATCH] KVM: x86: emulate SAHF instruction

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Date:	Thu, 31 Oct 2013 16:21:19 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: emulate SAHF instruction

On Thu, Oct 31, 2013 at 11:29:42AM +0100, Paolo Bonzini wrote:
> Yet another instruction that we fail to emulate, this time found
> in Windows 2008R2 32-bit.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
> 	Testcase on its way.  BTW, lahf/sahf is another candidate for
> 	#UD emulation.
> 
>  arch/x86/kvm/emulate.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 8e2a07bd8eac..ef750e75c930 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3296,6 +3296,18 @@ static int em_cpuid(struct x86_emulate_ctxt *ctxt)
>  	return X86EMUL_CONTINUE;
>  }
>  
> +static int em_sahf(struct x86_emulate_ctxt *ctxt)
> +{
> +	u32 flags;
> +
Shouldn't we check CPUID.80000001H.ECX[0] = 1 in 64 bit mode?

> +	flags = EFLG_CF | EFLG_PF | EFLG_AF | EFLG_ZF | EFLG_SF;
> +	flags &= *reg_rmw(ctxt, VCPU_REGS_RAX) >> 8;
> +
> +	ctxt->eflags &= ~0xffUL;
> +	ctxt->eflags |= flags | X86_EFLAGS_FIXED;
> +	return X86EMUL_CONTINUE;
> +}
> +
>  static int em_lahf(struct x86_emulate_ctxt *ctxt)
>  {
>  	*reg_rmw(ctxt, VCPU_REGS_RAX) &= ~0xff00UL;
> @@ -3788,7 +3800,7 @@ static const struct opcode opcode_table[256] = {
>  	DI(SrcAcc | DstReg, pause), X7(D(SrcAcc | DstReg)),
>  	/* 0x98 - 0x9F */
>  	D(DstAcc | SrcNone), I(ImplicitOps | SrcAcc, em_cwd),
> -	I(SrcImmFAddr | No64, em_call_far), N,
> +	I(SrcImmFAddr | No64, em_call_far), I(ImplicitOps, em_sahf),
>  	II(ImplicitOps | Stack, em_pushf, pushf),
>  	II(ImplicitOps | Stack, em_popf, popf), N, I(ImplicitOps, em_lahf),
>  	/* 0xA0 - 0xA7 */
> -- 
> 1.8.3.1

--
			Gleb.
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