From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757478AbYEPNiS (ORCPT ); Fri, 16 May 2008 09:38:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755448AbYEPNiG (ORCPT ); Fri, 16 May 2008 09:38:06 -0400 Received: from mx1.redhat.com ([66.187.233.31]:39056 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754259AbYEPNiF (ORCPT ); Fri, 16 May 2008 09:38:05 -0400 Date: Fri, 16 May 2008 09:36:58 -0400 From: Vivek Goyal To: "Huang, Ying" Cc: "Eric W. Biederman" , Pavel Machek , nigel@nigel.suspend2.net, "Rafael J. Wysocki" , Andrew Morton , linux-kernel@vger.kernel.org, Kexec Mailing List Subject: Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load Message-ID: <20080516133658.GE6926@redhat.com> References: <20080513053408.GA5870@redhat.com> <1210730266.23707.50.camel@caritas-dev.intel.com> <20080514025607.GA19944@redhat.com> <1210736275.23707.62.camel@caritas-dev.intel.com> <1210827473.23707.133.camel@caritas-dev.intel.com> <20080516020043.GC6926@redhat.com> <1210904374.23707.178.camel@caritas-dev.intel.com> <1210913568.23707.230.camel@caritas-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1210913568.23707.230.camel@caritas-dev.intel.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 16, 2008 at 12:52:48PM +0800, Huang, Ying wrote: > On Thu, 2008-05-15 at 19:55 -0700, Eric W. Biederman wrote: > > "Huang, Ying" writes: > > > > > The disadvantage of this solution is that kernel B must know it is > > > original kernel (A) or kexeced kernel (B). Different code should be used > > > by kernel A and kernel B. And after jump from A to B, jump from B to A, > > > when jump from A to B again, kernel A must use different code from the > > > first time. > > > > I don't know what the case is for keeping two kernels in memory and switching > > between them. > > This can be used to save the memory image of kernel B and accelerate the > hibernation. The real boot of kernel B is only needed first time. > > > I suspect a small piece of trampoline code between the two kernels could > > handle the case. (i.e. purgatory pays attention). > > > > That is a fundamental aspect of the design. A general purpose infrastructure > > with trampoline code to adapt it to whatever situation comes up. > > It is possible to use purgatory to deal with this problem. > > Jump from kernel A to kernel B > Jump to entry of purgatory (purgatory_entry) > purgatory save the return address (kexec_jump_back_entry_A) > Purgatory set kexec_jump_back_entry for kernel B to a code > segment in purgatory, say kexec_jump_back_entry_A_for_B > Purgatory jump to entry point of kernel B > Jump from kernel B to kernel A > Jump to purgatory (kexec_jump_back_entry_A_for_B) > Purgatory save the return address (kexec_jump_back_entry_B) > Purgatory return to kernel A (kexec_jump_back_entry_A) > Jump from kernel A to kernel B again > Jump to entry of purgatory (purgatory_entry) > Purgatory save the return address (kexec_jump_back_entry_A) > Purgatory jump to kexec_jump_back_entry_B > > The disadvantage of this solution is that some information is saved in > purgatory (kexec_jump_back_entry_A, kexec_jump_back_entry_B). So, > purgatory must be saved too when save the memory image of kernel A or > kernel B. Purgatory can be seen as a part of kernel B. But it is a > little tricky to think it as a part of kernel A too. That's a good point. Remembering the actual return points in purgatory will require purgatory to be saved along with core file. I think, purgatory is a good infrastructure for transitions between the kernels but at the same time, here it is a matter of just making a "call" and then inspecting the stack in kexec_jump_back_entry. IMHO, we can keep it simple and not involving purgatory in later transitions. Thanks Vivek