linux-kernel - Re: [PATCH] KVM: X86: avoid unused setup_syscalls

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Message-ID: <37dcc0bb-b624-4ea2-976a-51f5bfbd81a6@redhat.com>
Date:   Mon, 11 Nov 2019 15:08:16 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] KVM: X86: avoid unused setup_syscalls_segments call when
 SYSCALL check failed

On 09/11/19 09:58, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@...wei.com>
> 
> When SYSCALL/SYSENTER ability check failed, cs and ss is inited but
> remain not used. Delay initializing cs and ss until SYSCALL/SYSENTER
> ability check passed.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kvm/emulate.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 698efb8c3897..952d1a4f4d7e 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2770,11 +2770,10 @@ static int em_syscall(struct x86_emulate_ctxt *ctxt)
>  		return emulate_ud(ctxt);
>  
>  	ops->get_msr(ctxt, MSR_EFER, &efer);
> -	setup_syscalls_segments(ctxt, &cs, &ss);
> -
>  	if (!(efer & EFER_SCE))
>  		return emulate_ud(ctxt);
>  
> +	setup_syscalls_segments(ctxt, &cs, &ss);
>  	ops->get_msr(ctxt, MSR_STAR, &msr_data);
>  	msr_data >>= 32;
>  	cs_sel = (u16)(msr_data & 0xfffc);
> @@ -2838,12 +2837,11 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
>  	if (ctxt->mode == X86EMUL_MODE_PROT64)
>  		return X86EMUL_UNHANDLEABLE;
>  
> -	setup_syscalls_segments(ctxt, &cs, &ss);
> -
>  	ops->get_msr(ctxt, MSR_IA32_SYSENTER_CS, &msr_data);
>  	if ((msr_data & 0xfffc) == 0x0)
>  		return emulate_gp(ctxt, 0);
>  
> +	setup_syscalls_segments(ctxt, &cs, &ss);
>  	ctxt->eflags &= ~(X86_EFLAGS_VM | X86_EFLAGS_IF);
>  	cs_sel = (u16)msr_data & ~SEGMENT_RPL_MASK;
>  	ss_sel = cs_sel + 8;
> 

Queued, thanks.

Paolo