Re: [PATCH] KVM: nVMX: Replace kvm_set_cr0 with vmx_set_cr0 in load_vmcs12_host_state

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-02-24 09:56, Avi Kivity wrote:
> On Sat, Feb 23, 2013 at 11:57 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
>> On 2013-02-23 22:45, Nadav Har'El wrote:
>>> On Sat, Feb 23, 2013, Jan Kiszka wrote about "[PATCH] KVM: nVMX: Replace kvm_set_cr0 with vmx_set_cr0 in load_vmcs12_host_state":
>>>> -    kvm_set_cr0(vcpu, vmcs12->host_cr0);
>>>> +    vmx_set_cr0(vcpu, vmcs12->host_cr0);
>>>
>>> I don't remember now why I did this (and I'm not looking at the code),
>>> but this you'll need to really test carefully, including
>>> shadow-on-shadow mode (ept=0 in L0), to verify you're not missing any
>>> important side-effect of kvm_set_cr0.
>>>
>>> Also, if I remember correctly, during nVMX's review, Avi Kivity asked
>>> in several places that when I called vmx_set_cr0, I should instead call
>>> kvm_set_cr0(), because it does some extra stuff and does some extra
>>> checks. Hmm, see, see this:
>>>       http://markmail.org/message/hhidqyhbo2mrgxxc
>>>
>>> where Avi asked for the reverse patch you're attempting now.
>>
>> At least, kvm_set_cr0 can't be used as it assumes an otherwise
>> consistent guest state and an explicitly initiated transition - which is
>> naturally not the case while emulating a vmexit.
> 
> We have the same problem in KVM_SET_SREGS.

I don't see the problem. kvm_arch_vcpu_ioctl_set_sregs open-codes the
state update, not applying any transition checks.

Jan



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