linux-kernel - Re: [PATCH v3 12/28] KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot change

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Message-ID: <ZGQ2tslYJWSqpRh6@yzhao56-desk.sh.intel.com>
Date:   Wed, 17 May 2023 10:06:46 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.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 v3 12/28] KVM: x86/mmu: Don't rely on page-track
 mechanism to flush on memslot change

Reviewed-by: Yan Zhao <yan.y.zhao@...el.com>

On Fri, May 12, 2023 at 05:35:44PM -0700, Sean Christopherson wrote:
> Call kvm_mmu_zap_all_fast() directly when flushing a memslot instead of
> bouncing through the page-track mechanism.  KVM (unfortunately) needs to
> zap and flush all page tables on memslot DELETE/MOVE irrespective of
> whether KVM is shadowing guest page tables.
> 
> This will allow changing KVM to register a page-track notifier on the
> first shadow root allocation, and will also allow deleting the misguided
> kvm_page_track_flush_slot() hook itself once KVM-GT also moves to a
> different method for reacting to memslot changes.
> 
> No functional change intended.
> 
> Cc: Yan Zhao <yan.y.zhao@...el.com>
> Link: https://lore.kernel.org/r/20221110014821.1548347-2-seanjc@google.com
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 2e4476d38377..23a79723031b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -6184,13 +6184,6 @@ static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
>  	return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages));
>  }
>  
> -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;
> @@ -6208,7 +6201,6 @@ 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;
> @@ -6750,6 +6742,8 @@ 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);
> +
>  	kvm_page_track_flush_slot(kvm, slot);
>  }
>  
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>