Re: [PATCH v4 03/13] nEPT: Fix wrong test in kvm_set_cr3

[Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>]

On 07/25/2013 06:59 PM, Gleb Natapov wrote:
> From: Nadav Har'El <nyh@il.ibm.com>
> 
> kvm_set_cr3() attempts to check if the new cr3 is a valid guest physical
> address. The problem is that with nested EPT, cr3 is an *L2* physical
> address, not an L1 physical address as this test expects.
> 
> As the comment above this test explains, it isn't necessary, and doesn't
> correspond to anything a real processor would do. So this patch removes it.
> 
> Note that this wrong test could have also theoretically caused problems
> in nested NPT, not just in nested EPT. However, in practice, the problem
> was avoided: nested_svm_vmexit()/vmrun() do not call kvm_set_cr3 in the
> nested NPT case, and instead set the vmcb (and arch.cr3) directly, thus
> circumventing the problem. Additional potential calls to the buggy function
> are avoided in that we don't trap cr3 modifications when nested NPT is
> enabled. However, because in nested VMX we did want to use kvm_set_cr3()
> (as requested in Avi Kivity's review of the original nested VMX patches),
> we can't avoid this problem and need to fix it.
> 

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>