linux-kernel - Re: [PATCH V4 9/15] KVM: Add flush_link and parent_pte in the struct kvm_mmu

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Date:   Mon, 15 Oct 2018 12:12:07 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     lantianyu1986@...il.com
Cc:     Lan Tianyu <Tianyu.Lan@...rosoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        rkrcmar@...hat.com, devel@...uxdriverproject.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        michael.h.kelley@...rosoft.com, vkuznets@...hat.com
Subject: Re: [PATCH V4 9/15] KVM: Add flush_link and parent_pte in the struct
 kvm_mmu_page

On 13/10/2018 16:54, lantianyu1986@...il.com wrote:
> From: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> 
> PV EPT tlb flush function will accept a list of flush ranges and
> use struct kvm_mmu_page as the list entry.
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 19985c602ed6..8279235285f8 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -316,6 +316,7 @@ struct kvm_rmap_head {
>  
>  struct kvm_mmu_page {
>  	struct list_head link;
> +	struct list_head flush_link;

This can be an hlist.  However, you are not documenting what's the
locking here.  There are many places in which KVM does a
"cond_resched_lock(&vcpu->kvm->mmu_lock);" and you need to explain how
flush_link is not live across that.

I would start from a simpler patch that just uses the list-based flush
in kvm_mmu_commit_zap_page, where you already have the list of things to
flush as invalid_list.

>  	struct hlist_node hash_link;
>  	bool unsync;
>  
> 

Also this is not adding parent_pte, so the subject is incorrect.

Paolo