Re: [PATCH 1/3] KVM: MMU: Clean up set_spte()'s ACC_WRITE_MASK handling

[Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>]

On 05/09/2013 07:18 PM, Gleb Natapov wrote:
> On Thu, May 09, 2013 at 06:16:55PM +0800, Xiao Guangrong wrote:
>> On 05/09/2013 02:44 PM, Takuya Yoshikawa wrote:
>>> Rather than clearing the ACC_WRITE_MASK bit of pte_access in the
>>> "if (mmu_need_write_protect())" block not to call mark_page_dirty() in
>>> the following if statement, simply moving the call into the appropriate
>>> else block is better.
>>>
>>> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
>>> ---
>>>  arch/x86/kvm/mmu.c |    7 ++-----
>>>  1 files changed, 2 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>>> index 004cc87..08119a8 100644
>>> --- a/arch/x86/kvm/mmu.c
>>> +++ b/arch/x86/kvm/mmu.c
>>> @@ -2386,14 +2386,11 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>>>  			pgprintk("%s: found shadow page for %llx, marking ro\n",
>>>  				 __func__, gfn);
>>>  			ret = 1;
>>> -			pte_access &= ~ACC_WRITE_MASK;
>>>  			spte &= ~(PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE);
>>> -		}
>>> +		} else
>>> +			mark_page_dirty(vcpu->kvm, gfn);
>>>  	}
>>>
>>> -	if (pte_access & ACC_WRITE_MASK)
>>> -		mark_page_dirty(vcpu->kvm, gfn);
>>> -
>>>  set_pte:
>>>  	if (mmu_spte_update(sptep, spte))
>>>  		kvm_flush_remote_tlbs(vcpu->kvm);
>>
>> That function is really magic, and this change do no really help it. I had several
>> patches posted some months ago to make these kind of code better understanding, but
>> i am too tired to update them.
> Can you point me to them? Your work is really appreciated, I am sorry

There are two patches about this set_spte cleanups:

https://lkml.org/lkml/2013/1/23/125
https://lkml.org/lkml/2013/1/23/138

> you feel this way.

It is not your fault, it is mine.

Will update these patches when i finish the zap-all-page and zap-mmio-sp
related things.