linux-kernel - Re: [PATCH v3 03/11] KVM: x86: retry non-page-table writing instruction

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Message-ID: <4E707991.10705@redhat.com>
Date:	Wed, 14 Sep 2011 12:53:21 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 03/11] KVM: x86: retry non-page-table writing instruction

On 09/13/2011 09:24 PM, Xiao Guangrong wrote:
> >>
> >>  +static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
> >>  +                  unsigned long cr2,  int emulation_type)
> >>  +{
> >>  +    if (!vcpu->arch.mmu.direct_map&&   !mmu_is_nested(vcpu))
> >>  +        gpa = kvm_mmu_gva_to_gpa_write(vcpu, cr2, NULL);
> >
> >  If mmu_is_nested() cr2 is an ngpa, we have to translate it to a gpa, no?
> >
>
> Yeah, will fix it.
>
> And this bug also exists in the current code: it always uses L2 gpa to emulate
> write operation.

Can you please send this fix separately, so it can be backported if needed?

> I guess the reason that it is not triggered is: the gpa of L2's shadow page can
> not be touched by L2, it means no page table is write-protected by L2.

Yes.  All real guest hypervisors will do that.  But it is technically 
possible for a hypervisor to allow its guest access to the real page tables.

> >  btw, I don't see mmu.direct_map initialized for nested npt?
> >
>
> nested_svm_vmrun() ->  nested_svm_init_mmu_context():
> static int nested_svm_init_mmu_context(struct kvm_vcpu *vcpu)
> {
> 	int r;
>
> 	r = kvm_init_shadow_mmu(vcpu,&vcpu->arch.mmu);
>
> 	vcpu->arch.mmu.set_cr3           = nested_svm_set_tdp_cr3;
> 	vcpu->arch.mmu.get_cr3           = nested_svm_get_tdp_cr3;
> 	vcpu->arch.mmu.get_pdptr         = nested_svm_get_tdp_pdptr;
> 	vcpu->arch.mmu.inject_page_fault = nested_svm_inject_npf_exit;
> 	vcpu->arch.mmu.shadow_root_level = get_npt_level();
> 	vcpu->arch.walk_mmu              =&vcpu->arch.nested_mmu;
>
> 	return r;
> }
>
> It is initialized in kvm_init_shadow_mmu　:-)

Yes, need new eyeglasses.

-- 
error compiling committee.c: too many arguments to function

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