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

[Gleb Natapov <gleb@redhat.com>]

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
you feel this way.

--
			Gleb.