linux-kernel - Re: [PATCH RESEND v4 5/9] KVM: VMX: Add init/set/get functions for SPP

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Date:   Wed, 14 Aug 2019 22:34:01 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, rkrcmar@...hat.com,
        jmattson@...gle.com, yu.c.zhang@...el.com, alazar@...defender.com,
        pbonzini@...hat.com, sean.j.christopherson@...el.com
Subject: Re: [PATCH RESEND v4 5/9] KVM: VMX: Add init/set/get functions for
 SPP

On Wed, Aug 14, 2019 at 02:43:39PM +0200, Vitaly Kuznetsov wrote:
> Yang Weijiang <weijiang.yang@...el.com> writes:
> 
> > init_spp() must be called before {get, set}_subpage
> > functions, it creates subpage access bitmaps for memory pages
> > and issues a KVM request to setup SPPT root pages.
> >
> > kvm_mmu_set_subpages() is to enable SPP bit in EPT leaf page
> > and setup corresponding SPPT entries. The mmu_lock
> > is held before above operation. If it's called in EPT fault and
> > SPPT mis-config induced handler, mmu_lock is acquired outside
> > the function, otherwise, it's acquired inside it.
> >
> > kvm_mmu_get_subpages() is used to query access bitmap for
> > protected page, it's also used in EPT fault handler to check
> > whether the fault EPT page is SPP protected as well.
> >
> > Co-developed-by: He Chen <he.chen@...ux.intel.com>
> > Signed-off-by: He Chen <he.chen@...ux.intel.com>
> > Co-developed-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
> > Signed-off-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |  18 ++++
> >  arch/x86/include/asm/vmx.h      |   2 +
> >  arch/x86/kvm/mmu.c              | 160 ++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/vmx/vmx.c          |  48 ++++++++++
> >  arch/x86/kvm/x86.c              |  40 ++++++++
> >  include/linux/kvm_host.h        |   4 +-
> >  include/uapi/linux/kvm.h        |   9 ++
> >  7 files changed, 280 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 44f6e1757861..5c4882015acc 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -398,8 +398,13 @@ struct kvm_mmu {
> >  	void (*invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa);
> >  	void (*update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> >  			   u64 *spte, const void *pte);
> > +	int (*get_subpages)(struct kvm *kvm, struct kvm_subpage *spp_info);
> > +	int (*set_subpages)(struct kvm *kvm, struct kvm_subpage *spp_info);
> > +	int (*init_spp)(struct kvm *kvm);
> > +
> >  	hpa_t root_hpa;
> >  	gpa_t root_cr3;
> > +	hpa_t sppt_root;
> 
> (I'm sorry if this was previously discussed, I didn't look into previous
> submissions).
> 
> What happens when we launch a nested guest and switch vcpu->arch.mmu to
> point at arch.guest_mmu? sppt_root will point to INVALID_PAGE and SPP
> won't be enabled in VMCS?
> 
> (I'm sorry again, I'm likely missing something obvious)
> 
> -- 
> Vitaly

Hi, Vitaly,
Thanks for raising a good qeustion, I must have missed the nested case,
I'll double check how to support the nested case.