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

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Date:	Sun, 15 Apr 2012 18:16:31 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	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 04/13/2012 01:14 PM, Xiao Guangrong 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
> +#define PTE_LIST_DESC		(1 << PTE_LIST_DESC_BIT)
>  #define PTE_LIST_FLAG_MASK	(0x3ull)
>
>  static void
> @@ -1067,6 +1069,12 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu)
>  	return mmu_memory_cache_free_objects(cache);
>  }
>
> +static void host_page_write_protect(u64 *spte, unsigned long *rmapp)
> +{
> +	if (!(*spte & SPTE_HOST_WRITEABLE))
> +		__test_and_set_bit(PTE_LIST_WP_BIT, rmapp);
> +}
>

Why is this needed, in addition to spte.SPTE_WRITE_PROTECT?

-- 
error compiling committee.c: too many arguments to function

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