From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH v2 3/3] KVM: remove dummy pages Date: Thu, 26 Jul 2012 17:35:13 +0800 Message-ID: <50110F51.3050903@linux.vnet.ibm.com> References: <5010C008.4030304@linux.vnet.ibm.com> <5010C083.30102@linux.vnet.ibm.com> <5011062F.3080505@redhat.com> <20120726182033.e127e9e6.yoshikawa.takuya@oss.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Marcelo Tosatti , LKML , KVM To: Takuya Yoshikawa Return-path: Received: from e23smtp02.au.ibm.com ([202.81.31.144]:46802 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751061Ab2GZJfX (ORCPT ); Thu, 26 Jul 2012 05:35:23 -0400 Received: from /spool/local by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 26 Jul 2012 19:35:07 +1000 In-Reply-To: <20120726182033.e127e9e6.yoshikawa.takuya@oss.ntt.co.jp> Sender: kvm-owner@vger.kernel.org List-ID: On 07/26/2012 05:20 PM, Takuya Yoshikawa wrote: > On Thu, 26 Jul 2012 11:56:15 +0300 > Avi Kivity wrote: > >> Since my comments are better done as a separate patch, I applied all >> three patches. Thanks! > > Is this patch really safe for all architectures? > > IS_ERR_VALUE() casts -MAX_ERRNO to unsigned long and then does comparison. > Isn't it possible to conflict with valid pfns? > See IS_ERR_VALUE(): #define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO) The minimal value of the error code is: 0xffff f001 on 32-bit and 0x ffff ffff ffff f001 on 64-bit, it is fair larger that a valid pfn (for the pfn, the most top of 12 bits are always 0). Note, PAE is a special case, but only 64G physical memory is valid, 0xffff f001 is also suitable for that.