linux-kernel - Re: [PATCH 4/6] kvm: nVMX: support EPT accessed/dirty bits

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Date:   Fri, 14 Apr 2017 13:17:56 +0800
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Bandan Das <bsd@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, david@...hat.com
Subject: Re: [PATCH 4/6] kvm: nVMX: support EPT accessed/dirty bits



On 13/04/2017 07:02, Bandan Das wrote:
>> For EPT it is, you're right it's fishy.  The "nested_access" should be
>> computed in translate_nested_gpa, which is where kvm->arch.nested_mmu
>> (non-EPT) requests to access kvm->arch.mmu (EPT).
>
> Thanks for the clarification. Is it the case when L1 runs L2 without
> EPT ? I can't figure out the case where translate_nested_gpa will actually
> be called.

It happens when L2 instruction are emulated by L0, for example when L1
is passing through I/O ports to L2 and L2 runs an "insb" instruction.  I
think this case is not covered by vmx.flat.

Paolo

> FNAME(walk_addr_nested) calls walk_addr_generic
> with &vcpu->arch.nested_mmu and init_kvm_nested_mmu() sets gva_to_gpa()
> with the appropriate "_nested" functions. But the gva_to_gpa() pointers
> don't seem to get invoked at all for the nested case.
> 
> BTW, just noticed that setting PFERR_USER_MASK is redundant since
> translate_nested_gpa does it too.