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

Alexander Graf
2010-04-23T14:20:33Z

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@amd.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