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

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

[-- Attachment #1: Type: text/plain, Size: 1373 bytes --]

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.

However, there are some side effects that need a closer look, likely
also in other places where vmx_set_cr0 is used directly. E.g.
load_pdptrs. The lack of calling them on host->guest switch may explain
the PAE issues you once saw with your nEPT implementation.

OK, more work...

Jan



[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 263 bytes --]