linux-kernel - Re: [PATCH 3/3] KVM: MMU: track the refcount when unmap the page

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Date:	Tue, 3 Jul 2012 17:30:53 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] KVM: MMU: track the refcount when unmap the page

On Tue, Jul 03, 2012 at 02:32:14PM +0800, Xiao Guangrong wrote:
> It will trigger a WARN_ON if the page has been freed but it is still
> used in mmu, it can help us to detect mm bug early
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index cac3408..af7e076 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -527,6 +527,14 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
>  		return 0;
> 
>  	pfn = spte_to_pfn(old_spte);
> +
> +	/*
> +	 * KVM does not hold the refcount of the page used by
> +	 * kvm mmu, before reclaiming the page, we should
> +	 * unmap it from mmu first.
> +	 */
> +	WARN_ON(!page_count(pfn_to_page(pfn)));
> +

Except for mmio pfns.

Applied patch 1 and 2 to master, thanks.

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