linux-kernel - Re: [PATCH 09/24] kvm: x86/mmu: Don't redundantly clear TDP MMU pt memory

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Date:   Tue, 26 Jan 2021 15:14:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH 09/24] kvm: x86/mmu: Don't redundantly clear TDP MMU pt
 memory

On 12/01/21 19:10, Ben Gardon wrote:
> The KVM MMU caches already guarantee that shadow page table memory will
> be zeroed, so there is no reason to re-zero the page in the TDP MMU page
> fault handler.
> 
> No functional change intended.
> 
> Reviewed-by: Peter Feiner <pfeiner@...gle.com>
> 
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
>   arch/x86/kvm/mmu/tdp_mmu.c | 1 -
>   1 file changed, 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 411938e97a00..55df596696c7 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -665,7 +665,6 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>   			sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level);
>   			list_add(&sp->link, &vcpu->kvm->arch.tdp_mmu_pages);
>   			child_pt = sp->spt;
> -			clear_page(child_pt);
>   			new_spte = make_nonleaf_spte(child_pt,
>   						     !shadow_accessed_mask);
>   
> 

Queued, thanks.

Paolo