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Re: [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from kvm_mmu_get_page() to link_shadow_page()

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On 12/11/2015 12:56, Takuya Yoshikawa wrote:
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 9d21b44..f414ca6 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -598,7 +598,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
>  			goto out_gpte_changed;
>  
>  		if (sp)
> -			link_shadow_page(it.sptep, sp, PT_GUEST_ACCESSED_MASK);
> +			link_shadow_page(vcpu, it.sptep, sp, PT_GUEST_ACCESSED_MASK);
>  	}
>  

Here I think you can remove completely the

	if (sp)
		kvm_mmu_put_page(sp, it.sptep);

later in FNAME(fetch).  Apart from this nit, it's okay.

On to kvm_mmu_get_page...

        if (!direct) {
                if (rmap_write_protect(vcpu, gfn))
                        kvm_flush_remote_tlbs(vcpu->kvm);
                if (level > PT_PAGE_TABLE_LEVEL && need_sync)
                        kvm_sync_pages(vcpu, gfn);

This seems fishy.

need_sync is set if sp->unsync, but then the parents have not been
unsynced yet.

On the other hand, all calls to kvm_mmu_get_page except for the
roots are followed by link_shadow_page...  Perhaps if parent_pte != NULL
you can call link_shadow_page directly from kvm_mmu_get_page.  The call
would go before the "if (!direct)" and it would subsume all the existing
calls.

We could probably also warn if

	(parent_pte == NULL)
		!= (level == vcpu->arch.mmu.root_level)

in kvm_mmu_get_page.

Paolo
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[PATCH 00/10 V2] KVM: x86: MMU: Clean up x86's mmu code for future  work Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:40 +0100
  [PATCH 04/10] KVM: x86: MMU: Remove is_rmap_spte() and use  is_shadow_present_pte() Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:40 +0100
  [PATCH 01/10] KVM: x86: MMU: Remove unused parameter of  __direct_map() Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:40 +0100
  [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit in  unsync child bitmap Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:40 +0100
  [PATCH 08/10] KVM: x86: MMU: Move initialization of parent_ptes out  from kvm_mmu_alloc_page() Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:50 +0100
  [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from  kvm_mmu_get_page() to link_shadow_page() Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:50 +0100
    Re: [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from  kvm_mmu_get_page() to link_shadow_page() Paolo Bonzini <pbonzini@redhat.com> - 2015-11-12 15:30 +0100
      Re: [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from  kvm_mmu_get_page() to link_shadow_page() Paolo Bonzini <pbonzini@redhat.com> - 2015-11-12 18:10 +0100
      Re: [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from  kvm_mmu_get_page() to link_shadow_page() Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-13 03:20 +0100
        Re: [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from  kvm_mmu_get_page() to link_shadow_page() Paolo Bonzini <pbonzini@redhat.com> - 2015-11-13 12:00 +0100
  [PATCH 06/10] KVM: x86: MMU: Consolidate WARN_ON/BUG_ON checks for  reverse-mapped sptes Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:50 +0100
    Re: [PATCH 06/10] KVM: x86: MMU: Consolidate WARN_ON/BUG_ON checks  for reverse-mapped sptes Marcelo Tosatti <mtosatti@redhat.com> - 2015-11-13 23:10 +0100
      Re: [PATCH 06/10] KVM: x86: MMU: Consolidate WARN_ON/BUG_ON checks  for reverse-mapped sptes Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-16 04:40 +0100
  [PATCH 10/10] KVM: x86: MMU: Remove unused parameter parent_pte  from kvm_mmu_get_page() Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:50 +0100
  [PATCH 07/10] KVM: x86: MMU: Encapsulate the type of rmap-chain  head in a new struct Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-12 12:50 +0100
  Re: [PATCH 00/10 V2] KVM: x86: MMU: Clean up x86's mmu code for  future work Paolo Bonzini <pbonzini@redhat.com> - 2015-11-12 13:10 +0100

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