linux-kernel - Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO

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Message-ID: <4CE33321.10207@cn.fujitsu.com>
Date:	Wed, 17 Nov 2010 09:42:57 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W
 to RO

On 11/17/2010 04:24 AM, Marcelo Tosatti wrote:
> On Fri, Nov 12, 2010 at 06:30:22PM +0800, Xiao Guangrong wrote:
>> We just need flush tlb if overwrite a writable spte with a read-only one
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
>> ---
>>  arch/x86/kvm/mmu.c |   19 +++++++++----------
>>  1 files changed, 9 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 4b6d54c..1a93ab4 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -2044,6 +2044,15 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>>  	if (pte_access & ACC_WRITE_MASK)
>>  		mark_page_dirty(vcpu->kvm, gfn);
>>  
>> +	/*
>> +	 * If we overwrite a writable spte with a read-only one,
>> +	 * 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.
>> +	 */
>> +	else if (is_writable_pte(*sptep))
>> +		ret = 1;
>> +
> 
> The return value of set_spte indicates whether the gfn being mapped to
> was write protected, not if a TLB flush is necessary.
> 

Yes, i also noticed this and have fixed in the v2 queue, thanks Marcelo!
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