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 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.