linux-kernel - Re: [PATCH v2 2/6] KVM: MMU: don't drop spte if overwrite it from W to RO

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Message-ID: <4CE4D1F8.7090701@cn.fujitsu.com>
Date:	Thu, 18 Nov 2010 15:12:56 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] KVM: MMU: don't drop spte if overwrite it from
 W to RO

On 11/17/2010 11:57 PM, Avi Kivity wrote:

>>>   set_pte:
>>>       update_spte(sptep, spte);
>>> +    /*
>>> +     * If we overwrite a writable spte with a read-only one we
>>> +     * should flush remote TLBs. Otherwise rmap_write_protect
>>> +     * will find a read-only spte, even though the writable spte
>>> +     * might be cached on a CPU's TLB.
>>> +     */
>>> +    if (is_writable_pte(entry)&&  !is_writable_pte(*sptep))
>>> +        kvm_flush_remote_tlbs(vcpu->kvm);
>> There is no need to flush on sync_page path since the guest is
>> responsible for it.
>>
> 
>  If we don't, the next rmap_write_protect() will incorrectly decide that
> there's no need to flush tlbs.
> 

Maybe it's not a problem if guest can flush all tlbs after overwrite it?
Marcelo, what's your comment about this?
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