From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 08/13] KVM: MMU: fask check whether page is writable Date: Sun, 01 Apr 2012 18:52:01 +0300 Message-ID: <4F7879A1.2020301@redhat.com> References: <4F742951.7080003@linux.vnet.ibm.com> <4F742A74.1050304@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM To: Xiao Guangrong Return-path: In-Reply-To: <4F742A74.1050304@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 03/29/2012 11:25 AM, Xiao Guangrong wrote: > Using PTE_LIST_WRITE_PROTECT bit in rmap store the write-protect status to > avoid unnecessary shadow page walking > > Also if no shadow page is indirect, the page is write-free > > > @@ -2262,6 +2291,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, > } > if (need_unsync) > kvm_unsync_pages(vcpu, gfn); > + > + *rmap &= ~PTE_LIST_WRITE_PROTECT; > + > So what are the rules for PTE_LIST_WRITE_PROTECT? Is is a cache for the mmu_need_write_protect? I'd like to understand it, I guess it can be set while write protection is unneeded, and cleared on the next check? Maybe split into two functions, one the normal mmu_need_write_protect (but renamed) and a new mmu_need_write_protect(), with locked and unlocked variants, calling the old one. -- error compiling committee.c: too many arguments to function