linux-kernel - Re: [PATCH v2 2/9] x86/kvm/mmu.c: set get_pdptr hook in kvm_init_shadow_ept

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Date:   Wed, 26 Sep 2018 19:16:02 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/9] x86/kvm/mmu.c: set get_pdptr hook in kvm_init_shadow_ept_mmu()

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> On Tue, Sep 25, 2018 at 07:58:37PM +0200, Vitaly Kuznetsov wrote:
>> kvm_init_shadow_ept_mmu() doesn't set get_pdptr() hook and is this
>> not a problem just because MMU context is already initialized and this
>> hook points to kvm_pdptr_read(). As we're intended to use a dedicated
>> MMU for shadow EPT MMU set this hook explicitly.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>> ---
>>  arch/x86/kvm/mmu.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index ca79ec0d8060..2bdc63f67886 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -4846,6 +4846,8 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
>>  	context->root_level = PT64_ROOT_4LEVEL;
>>  	context->direct_map = false;
>>  	context->base_role.word = root_page_role.word & mmu_base_role_mask.word;
>> +	context->get_pdptr = kvm_pdptr_read;
>
> Would it make sense to set this in nested_ept_init_mmu_context()
> along with set_cr3, get_cr3 and inject_page_fault?  The other MMU
> flows set them as a package deal.

Well, kvm_init_shadow_ept_mmu() has only one call site and reading the
code I was under an impression we set set_cr3/get_cr3/inject_page_fault
in vmx.c just to avoid passing all these vmx-specific functions as
pointers to kvm_init_shadow_ept_mmu(). With get_pdptr() I was thinking
"oh, great, this is not vmx-specific so we can set it in mmu.c" - but I
see your point and I'm ready to budge :-)

>
> Either way...
>
> Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>

Thanks!

>
>> +
>>  	update_permission_bitmask(vcpu, context, true);
>>  	update_pkru_bitmask(vcpu, context, true);
>>  	update_last_nonleaf_level(vcpu, context);

-- 
Vitaly