From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 09/11] KVM: MMU: simplify mmu_need_write_protect Date: Tue, 15 Dec 2015 17:25:10 +0800 Message-ID: <566FDC76.1090703@linux.intel.com> References: <1448907973-36066-1-git-send-email-guangrong.xiao@linux.intel.com> <1448907973-36066-10-git-send-email-guangrong.xiao@linux.intel.com> <566FD2A1.7010601@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Kai Huang , pbonzini@redhat.com Return-path: In-Reply-To: <566FD2A1.7010601@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 12/15/2015 04:43 PM, Kai Huang wrote: > > > On 12/01/2015 02:26 AM, Xiao Guangrong wrote: >> Now, all non-leaf shadow page are page tracked, if gfn is not tracked >> there is no non-leaf shadow page of gfn is existed, we can directly >> make the shadow page of gfn to unsync >> >> Signed-off-by: Xiao Guangrong >> --- >> arch/x86/kvm/mmu.c | 26 ++++++++------------------ >> 1 file changed, 8 insertions(+), 18 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 5a2ca73..f89e77f 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -2461,41 +2461,31 @@ static void __kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) >> kvm_mmu_mark_parents_unsync(sp); >> } >> -static void kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn) >> +static bool kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, >> + bool can_unsync) >> { >> struct kvm_mmu_page *s; >> for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) { >> + if (!can_unsync) >> + return true; > How about moving this right before for_each_gfn_indirect_valid_sp? As can_unsync is passed as > parameter, so there's no point checking it several times. > We can not do this. What we are doing here is checking if we have shadow page mapping for 'gfn': a) if no, it can be writable. b) if yes, check 'can_unsync' to see if these shadow pages can make to be 'unsync'. Your suggestion can break the point a). > A further thinking is can we move it to mmu_need_write_protect? Passing can_unsync as parameter to > kvm_unsync_pages sounds a little bit odd. > >> + >> if (s->unsync) >> continue; >> WARN_ON(s->role.level != PT_PAGE_TABLE_LEVEL); > How about large page mapping? Such as if guest uses 2M mapping and its shadow is indirect, does > above WARN_ON still meet? As you removed the PT level check in mmu_need_write_protect. The lager mapping are on the non-leaf shadow pages which can be figured out by kvm_page_track_check_mode() before we call this function.