linux-kernel - Re: [PATCH v2 11/27] KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot change

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Message-ID: <ZBHlIuhED8y3JIu1@google.com>
Date:   Wed, 15 Mar 2023 08:32:50 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v2 11/27] KVM: x86/mmu: Don't rely on page-track mechanism
 to flush on memslot change

On Wed, Mar 15, 2023, Yan Zhao wrote:
> On Fri, Mar 10, 2023 at 04:22:42PM -0800, Sean Christopherson wrote:
> ...
> > -static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,
> > -			struct kvm_memory_slot *slot,
> > -			struct kvm_page_track_notifier_node *node)
> > -{
> > -	kvm_mmu_zap_all_fast(kvm);
> > -}
> > -
> >  int kvm_mmu_init_vm(struct kvm *kvm)
> >  {
> >  	struct kvm_page_track_notifier_node *node = &kvm->arch.mmu_sp_tracker;
> > @@ -6110,7 +6103,6 @@ int kvm_mmu_init_vm(struct kvm *kvm)
> >  	}
> >  
> >  	node->track_write = kvm_mmu_pte_write;
> > -	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
> >  	kvm_page_track_register_notifier(kvm, node);
> >  
> >  	kvm->arch.split_page_header_cache.kmem_cache = mmu_page_header_cache;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index f706621c35b8..29dd6c97d145 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12662,6 +12662,8 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm)
> >  void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
> >  				   struct kvm_memory_slot *slot)
> >  {
> > +	kvm_mmu_zap_all_fast(kvm);
> Could we still call kvm_mmu_invalidate_zap_pages_in_memslot() here?
> As I know, for TDX, its version of
> kvm_mmu_invalidate_zap_pages_in_memslot() is like
> 
> static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,
>                         struct kvm_memory_slot *slot,
>                         struct kvm_page_track_notifier_node *node)
> {
>         if (kvm_gfn_shared_mask(kvm))
>                 kvm_mmu_zap_memslot(kvm, slot);
>         else
>                 kvm_mmu_zap_all_fast(kvm);
> }
> 
> Maybe this kind of judegment is better to be confined in mmu.c?

Hmm, yeah, I agree.  The only reason I exposed kvm_mmu_zap_all_fast() is because
kvm_mmu_zap_all() is already exposed for kvm_arch_flush_shadow_all() and it felt
weird/wrong to split those.  But that's the only usage of kvm_mmu_zap_all(), so
a better approach to maintain consistency would be to move
kvm_arch_flush_shadow_{all,memslot}() into mmu.c.  I'll do that in the next version.