Return-path: Received: from mga11.intel.com ([192.55.52.93]) by bombadil.infradead.org with esmtp (Exim 4.68 #1 (Red Hat Linux)) id 1JwVRF-0005WJ-R4 for kexec@lists.infradead.org; Thu, 15 May 2008 04:51:34 +0000 Subject: Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load From: "Huang, Ying" In-Reply-To: References: <1210574441.30365.8.camel@caritas-dev.intel.com> <20080513053408.GA5870@redhat.com> <1210730266.23707.50.camel@caritas-dev.intel.com> <20080514025607.GA19944@redhat.com> <1210736275.23707.62.camel@caritas-dev.intel.com> Date: Thu, 15 May 2008 12:57:53 +0800 Message-ID: <1210827473.23707.133.camel@caritas-dev.intel.com> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: "Eric W. Biederman" Cc: nigel@nigel.suspend2.net, Kexec Mailing List , linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Pavel Machek , Andrew Morton , Vivek Goyal On Wed, 2008-05-14 at 14:43 -0700, Eric W. Biederman wrote: [...] > Then as a preliminary design let's plan on this. > > - Pass the rentry point as the return address (using the C ABI). > We may want to load the stack pointer etc so we can act as > a direct entry point for new code. There are some issues about passing entry point as return address. The kexec jump (or kexec with return) is used for - Switching between original kernel (A) and kexeced kernel (B) - Call some code (such as BIOS code) in physical mode 1) When call some code in physical mode, the called code can use a simple return to return to kernel A. So there is no return address on stack after return to kernel A. Instead, argument 1 is on stack top. 2) When switch back from kernel B to kernel A, kernel B will call the jump back entry of kernel A with C ABI. So, the return address is on stack top. And kernel A get jump back entry of kernel B via the return address. Because the stack state is different between 1) and 2), the jump back entry of kernel A should distinguish them. Possible solution can be as follow: a) Before kernel A call some physical mode code or kernel B, it set argument 1 to be a magic number that can not be return address (such as -1). Jump back entry of kernel A can check whether the stack top is argument 1 or return address. b) Distinguish by return address. Such as, called physical mode code must return 0, while kernel B must set %eax to some other number. c) Use different entry point for 1) and 2). Two entry points are deduced from return address. Such as: entry1 = return_address; entry2 = return_address & ~0xfff; /* page aligned */ entry1 is used by physical mode code. entry2 is used by kernel B. Which one is better? Or some other solution? Best Regards, Huang Ying _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec