linux-kernel - Re: [PATCH 08/13] KVM: MMU: fask check whether page is writable

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Message-ID: <4F7879A1.2020301@redhat.com>
Date:	Sun, 01 Apr 2012 18:52:01 +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 08/13] KVM: MMU: fask check whether page is writable

On 03/29/2012 11:25 AM, Xiao Guangrong wrote:
> Using PTE_LIST_WRITE_PROTECT bit in rmap store the write-protect status to
> avoid unnecessary shadow page walking
>
> Also if no shadow page is indirect, the page is write-free
>
>
> @@ -2262,6 +2291,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
>  	}
>  	if (need_unsync)
>  		kvm_unsync_pages(vcpu, gfn);
> +
> +	*rmap &= ~PTE_LIST_WRITE_PROTECT;
> +
>

So what are the rules for PTE_LIST_WRITE_PROTECT?  Is is a cache for the
mmu_need_write_protect?

I'd like to understand it, I guess it can be set while write protection
is unneeded, and cleared on the next check?

Maybe split into two functions, one the normal mmu_need_write_protect
(but renamed) and a new mmu_need_write_protect(), with locked and
unlocked variants, calling the old one.

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

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