From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH] mm: mmu_notifier: fix inconsistent memory between secondary MMU and host Date: Wed, 22 Aug 2012 13:37:59 +0800 Message-ID: <50347037.3040209@linux.vnet.ibm.com> References: <503358FF.3030009@linux.vnet.ibm.com> <20120821150618.GJ27696@redhat.com> <50345735.2000807@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Andrea Arcangeli , Andrew Morton , Avi Kivity , Marcelo Tosatti , LKML , KVM , Linux Memory Management List To: Hugh Dickins Return-path: Received: from e28smtp06.in.ibm.com ([122.248.162.6]:52961 "EHLO e28smtp06.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754091Ab2HVFiK (ORCPT ); Wed, 22 Aug 2012 01:38:10 -0400 Received: from /spool/local by e28smtp06.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 22 Aug 2012 11:08:07 +0530 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 08/22/2012 12:12 PM, Hugh Dickins wrote: > On Wed, 22 Aug 2012, Xiao Guangrong wrote: >> On 08/21/2012 11:06 PM, Andrea Arcangeli wrote: >>> >>> The KSM usage of it looks safe because it will only establish readonly >>> ptes with it. >> >> Hmm, in KSM code, i found this code in replace_page: >> >> set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot)); >> >> It is possible to establish a writable pte, no? > > No: we only do KSM in private vmas (!VM_SHARED), and because of the > need to CopyOnWrite in those, vm_page_prot excludes write permission: > write permission has to be added on COW fault. After read the code carefully, yes, you are right. Thank you very much for your explanation, Hugh! :)