From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH] KVM: VMX: Do not overwrite vcpu->srcu_idx in
 vmx_vcpu_reset
Date: Thu, 14 Mar 2013 17:00:04 +0200
Message-ID: <20130314150004.GX11223@redhat.com>
References: <5141E41B.8080804@siemens.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Marcelo Tosatti <mtosatti@redhat.com>, kvm <kvm@vger.kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:38731 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1757653Ab3CNPAs (ORCPT <rfc822;kvm@vger.kernel.org>);
	Thu, 14 Mar 2013 11:00:48 -0400
Content-Disposition: inline
In-Reply-To: <5141E41B.8080804@siemens.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Thu, Mar 14, 2013 at 03:52:11PM +0100, Jan Kiszka wrote:
> vmx_vcpu_reset may now be called while already holding the srcu lock, so
> we may overwrite what was already saved there. Also, we lock and unlock
> in the same context, thus there was no need to save to the vcpu anyway.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Marcelo just suggested this as the simplest fix for the issue caused by
> the INIT/SIPI patch. Avoiding srcu lock for TSS handling might still be
> possible but more tricky.
> 
>  arch/x86/kvm/vmx.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 958ac3a..be5b1dc 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4117,6 +4117,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	u64 msr;
> +	int idx;
>  
>  	vmx->rmode.vm86_active = 0;
>  
> @@ -4190,9 +4191,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>  		vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
>  
>  	vmx->vcpu.arch.cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
> -	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> +	idx = srcu_read_lock(&vcpu->kvm->srcu);
>  	vmx_set_cr0(&vmx->vcpu, kvm_read_cr0(vcpu)); /* enter rmode */
> -	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> +	srcu_read_unlock(&vcpu->kvm->srcu, idx);
vmx_set_cr0() does:
                srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
                vmx_set_tss_addr(vcpu->kvm, 0xfeffd000);
                vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
So with this change the sequence will be:

vcpu->srcu_idx = srcu_read_lock()
  idx = srcu_read_lock(&vcpu->kvm->srcu); 
   srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
   vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
  srcu_read_unlock(&vcpu->kvm->srcu, idx);
srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);

Not sure this is valid.

>  	vmx_set_cr4(&vmx->vcpu, 0);
>  	vmx_set_efer(&vmx->vcpu, 0);
>  	vmx_fpu_activate(&vmx->vcpu);
> -- 
> 1.7.3.4

--
			Gleb.