linux-kernel - Re: [PATCH v2 01/12] KVM: MMU: lazily drop large spte

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Message-ID: <51073AB7.3050207@linux.vnet.ibm.com>
Date:	Tue, 29 Jan 2013 10:57:59 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Avi Kivity <avi.kivity@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 01/12] KVM: MMU: lazily drop large spte

On 01/27/2013 08:06 PM, Gleb Natapov wrote:
> On Wed, Jan 23, 2013 at 06:04:17PM +0800, Xiao Guangrong wrote:
>> Do not drop large spte until it can be insteaded by small pages so that
>> the guest can happliy read memory through it
>>
>> The idea is from Avi:
>> | As I mentioned before, write-protecting a large spte is a good idea,
>> | since it moves some work from protect-time to fault-time, so it reduces
>> | jitter.  This removes the need for the return value.
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> ---
>>  arch/x86/kvm/mmu.c |   21 ++++++---------------
>>  1 files changed, 6 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 9f628f7..0f90269 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -1105,7 +1105,7 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
>>
>>  /*
>>   * Write-protect on the specified @sptep, @pt_protect indicates whether
>> - * spte writ-protection is caused by protecting shadow page table.
>> + * spte write-protection is caused by protecting shadow page table.
>>   * @flush indicates whether tlb need be flushed.
>>   *
>>   * Note: write protection is difference between drity logging and spte
>> @@ -1114,31 +1114,23 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
>>   *   its dirty bitmap is properly set.
>>   * - for spte protection, the spte can be writable only after unsync-ing
>>   *   shadow page.
>> - *
>> - * Return true if the spte is dropped.
>>   */
>> -static bool
>> +static void
>>  spte_write_protect(struct kvm *kvm, u64 *sptep, bool *flush, bool pt_protect)
> Since return value is not longer used make the function return true if flush is needed
> instead of returning it via pointer to a variable.

Right, i forgot to check it, will update it in the next version. Thanks for your pointing
it out.


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