linux-kernel - Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap

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Message-ID: <4BC2D8D6.6030306@redhat.com>
Date:	Mon, 12 Apr 2010 11:24:54 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path

On 04/12/2010 11:01 AM, Xiao Guangrong wrote:
> - calculate zapped page number properly in mmu_zap_unsync_children()
> - calculate freeed page number properly kvm_mmu_change_mmu_pages()
> - restart list walking if have children page zapped
>
> Signed-off-by: Xiao Guangrong<xiaoguangrong@...fujitsu.com>
> ---
>   arch/x86/kvm/mmu.c |    7 ++++---
>   1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index a23ca75..8f4f781 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1483,8 +1483,8 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
>   		for_each_sp(pages, sp, parents, i) {
>   			kvm_mmu_zap_page(kvm, sp);
>   			mmu_pages_clear_parents(&parents);
> +			zapped++;
>   		}
> -		zapped += pages.nr;
>   		kvm_mmu_pages_init(parent,&parents,&pages);
>   	}
>    

This looks correct, I don't understand how we work in the first place.  
Marcelo?

> @@ -1540,7 +1540,7 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages)
>
>   			page = container_of(kvm->arch.active_mmu_pages.prev,
>   					    struct kvm_mmu_page, link);
> -			kvm_mmu_zap_page(kvm, page);
> +			used_pages -= kvm_mmu_zap_page(kvm, page);
>   			used_pages--;
>   		}
>    

This too.  Wow.

>   		kvm->arch.n_free_mmu_pages = 0;
> @@ -1589,7 +1589,8 @@ static void mmu_unshadow(struct kvm *kvm, gfn_t gfn)
>   		&&  !sp->role.invalid) {
>   			pgprintk("%s: zap %lx %x\n",
>   				 __func__, gfn, sp->role.word);
> -			kvm_mmu_zap_page(kvm, sp);
> +			if (kvm_mmu_zap_page(kvm, sp))
> +				nn = bucket->first;
>   		}
>   	}
>    

I don't understand why this is needed.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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