From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Date: Fri, 31 Aug 2018 07:33:52 -0700 Message-ID: <1535726032.32537.0.camel@intel.com> References: <1535649960.26689.15.camel@intel.com> <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> <1535651666.27823.6.camel@intel.com> <1535660494.28258.36.camel@intel.com> <1535662366.28781.6.camel@intel.com> <20180831095300.GF24124@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180831095300.GF24124@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra , Jann Horn Cc: Dave Hansen , the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek List-Id: linux-arch.vger.kernel.org On Fri, 2018-08-31 at 11:53 +0200, Peter Zijlstra wrote: > On Thu, Aug 30, 2018 at 11:47:16PM +0200, Jann Horn wrote: > > > >         do { > >                 pte = pte_wrprotect(pte); > >                 /* note: relies on _PAGE_DIRTY_HW < _PAGE_DIRTY_SW > > */ > >                 /* dirty direct bit-twiddling; you can probably > > write > > this in a nicer way */ > >                 pte.pte |= (pte.pte & _PAGE_DIRTY_HW) >> > > _PAGE_BIT_DIRTY_HW << _PAGE_BIT_DIRTY_SW; > >                 pte.pte &= ~_PAGE_DIRTY_HW; > >                 pte = cmpxchg(ptep, pte, new_pte); > >         } while (pte != new_pte); > Please use the form: > > pte_t new_pte, pte = READ_ONCE(*ptep); > do { > new_pte = /* ... */; > } while (!try_cmpxchg(ptep, &pte, new_pte); > > Also, this will fail to build on i386-PAE, but I suspect this code > will > be under some CONFIG option specific to x86_64 anyway. Thanks!  I will work on it. Yu-cheng From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga18.intel.com ([134.134.136.126]:42997 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728627AbeHaSp4 (ORCPT ); Fri, 31 Aug 2018 14:45:56 -0400 Message-ID: <1535726032.32537.0.camel@intel.com> Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW From: Yu-cheng Yu Date: Fri, 31 Aug 2018 07:33:52 -0700 In-Reply-To: <20180831095300.GF24124@hirez.programming.kicks-ass.net> References: <1535649960.26689.15.camel@intel.com> <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> <1535651666.27823.6.camel@intel.com> <1535660494.28258.36.camel@intel.com> <1535662366.28781.6.camel@intel.com> <20180831095300.GF24124@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra , Jann Horn Cc: Dave Hansen , the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com Message-ID: <20180831143352.lVkUhgc4hu-QDxFd18CMpWXXoXAAJ6X1enJhUZxk6rg@z> On Fri, 2018-08-31 at 11:53 +0200, Peter Zijlstra wrote: > On Thu, Aug 30, 2018 at 11:47:16PM +0200, Jann Horn wrote: > > > >         do { > >                 pte = pte_wrprotect(pte); > >                 /* note: relies on _PAGE_DIRTY_HW < _PAGE_DIRTY_SW > > */ > >                 /* dirty direct bit-twiddling; you can probably > > write > > this in a nicer way */ > >                 pte.pte |= (pte.pte & _PAGE_DIRTY_HW) >> > > _PAGE_BIT_DIRTY_HW << _PAGE_BIT_DIRTY_SW; > >                 pte.pte &= ~_PAGE_DIRTY_HW; > >                 pte = cmpxchg(ptep, pte, new_pte); > >         } while (pte != new_pte); > Please use the form: > > pte_t new_pte, pte = READ_ONCE(*ptep); > do { > new_pte = /* ... */; > } while (!try_cmpxchg(ptep, &pte, new_pte); > > Also, this will fail to build on i386-PAE, but I suspect this code > will > be under some CONFIG option specific to x86_64 anyway. Thanks!  I will work on it. Yu-cheng