linux-kernel - Re: [PATCH 3/8] KVM: SVM: Sync cr0 and cr3 to kvm state before nested handling

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Date:	Fri, 23 Apr 2010 16:20:28 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] KVM: SVM: Sync cr0 and cr3 to kvm state before nested handling


On 23.04.2010, at 16:17, Joerg Roedel wrote:

> On Fri, Apr 23, 2010 at 03:50:20PM +0200, Alexander Graf wrote:
>> 
>> On 22.04.2010, at 12:33, Joerg Roedel wrote:
>> 
>>> This patch syncs cr0 and cr3 from the vmcb to the kvm state
>>> before nested intercept handling is done. This allows to
>>> simplify the vmexit path.
>>> 
>>> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
>>> ---
>>> arch/x86/kvm/svm.c |   15 ++++++---------
>>> 1 files changed, 6 insertions(+), 9 deletions(-)
>>> 
>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>> index c480d7f..5ad9d80 100644
>>> --- a/arch/x86/kvm/svm.c
>>> +++ b/arch/x86/kvm/svm.c
>>> @@ -1799,10 +1799,7 @@ static int nested_svm_vmexit(struct vcpu_svm *svm)
>>> 	nested_vmcb->save.gdtr   = vmcb->save.gdtr;
>>> 	nested_vmcb->save.idtr   = vmcb->save.idtr;
>>> 	nested_vmcb->save.cr0    = kvm_read_cr0(&svm->vcpu);
>>> -	if (npt_enabled)
>>> -		nested_vmcb->save.cr3    = vmcb->save.cr3;
>>> -	else
>>> -		nested_vmcb->save.cr3    = svm->vcpu.arch.cr3;
>>> +	nested_vmcb->save.cr3    = svm->vcpu.arch.cr3;
>> 
>> 
>> Why don't we need this anymore again?
> 
> Because arch.cr3 contains always the current l2-cr3. This wasn't the
> case before because the sync was done after the nested handling. But now
> we do it before a vmexit can happen and are safe to just use arch.cr3.

I see.


Alex

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