linux-kernel - Re: [PATCH 00/13] KVM: MMU: fast page fault

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Date:	Mon, 09 Apr 2012 17:25:19 +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 00/13] KVM: MMU: fast page fault

On 04/09/2012 04:55 PM, Xiao Guangrong wrote:
>
> Okay, let's simplify it as possible:
>
> - let it only fix the page fault with PFEC.P == 1 && PFEC.W = 0, that means
>   unlock set_spte path can be dropped
>
> - let it just fixes the page fault caused by dirty-log that means we always
>   skip the spte which write-protected by shadow page protection.
>
> Then, things should be fair simper:
>
> In set_spte path, if the spte can be writable, we set ALLOW_WRITE bit
> In rmap_write_protect:
>   if (spte.PT_WRITABLE_MASK) {
> 	WARN_ON(!(spte & ALLOW_WRITE));
> 	spte &= ~PT_WRITABLE_MASK;
> 	spte |= WRITE_PROTECT;
>   }
>
> in fast page fault:
>
> if (spte & PT_WRITABLE_MASK)
> 	return_go_guest;
>
> if ((spte & ALLOW_WRITE) && !(spte & WRITE_PROTECT))
> 	cmpxchg spte + PT_WRITABLE_MASK
>
> The information all we needed comes from spte it is independence from other path,
> and no barriers.
>
>
> Hmm, how about this one?
>

I like it. WRITE_PROTECT is better than my ALLOW_WRITES, the meaning is
clearer.

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

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