linux-kernel - Re: [PATCH v2 10/16] KVM: MMU: fask check whether page is writable

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Date:	Sat, 14 Apr 2012 12:01:53 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 10/16] KVM: MMU: fask check whether page is writable

On Fri, 13 Apr 2012 18:14:26 +0800
Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:

> Using bit 1 (PTE_LIST_WP_BIT) in rmap store the write-protect status
> to avoid unnecessary shadow page walking
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c |   40 ++++++++++++++++++++++++++++++++++------
>  1 files changed, 34 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 0c6e92d..8b71908 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -796,7 +796,9 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn)
>  	return level - 1;
>  }
> 
> -#define PTE_LIST_DESC		(0x1ull)
> +#define PTE_LIST_DESC_BIT	0
> +#define PTE_LIST_WP_BIT	1

_BIT ?

> +#define PTE_LIST_DESC		(1 << PTE_LIST_DESC_BIT)
>  #define PTE_LIST_FLAG_MASK	(0x3ull)
> 

Well, I think that rmap is losing its original meaning:
Before, it held just the information needed to link spteps.

Now it has more roles, and getting kind of descriptor?

...

> @@ -2291,9 +2310,15 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
>  {
>  	struct kvm_mmu_page *s;
>  	struct hlist_node *node;
> +	unsigned long *rmap;
>  	bool need_unsync = false;
> 
> +	rmap = gfn_to_rmap(vcpu->kvm, gfn, PT_PAGE_TABLE_LEVEL);

Please use consistent variable names.

In other parts of this patch, you are using rmapp for this.

	Takuya
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