From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751946AbbALWRV (ORCPT ); Mon, 12 Jan 2015 17:17:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40446 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132AbbALWRT (ORCPT ); Mon, 12 Jan 2015 17:17:19 -0500 Date: Mon, 12 Jan 2015 17:16:34 -0500 From: Vivek Goyal To: "Michael Kerrisk (man-pages)" Cc: lkml , "linux-man@vger.kernel.org" , kexec@lists.infradead.org, Andy Lutomirski , Dave Young , "H. Peter Anvin" , Borislav Petkov , "Eric W. Biederman" Subject: Re: Edited kexec_load(2) [kexec_file_load()] man page for review Message-ID: <20150112221634.GD16162@redhat.com> References: <545FBDDD.9060801@gmail.com> <20141111213037.GA31445@redhat.com> <54ADA284.30502@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54ADA284.30502@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 07, 2015 at 10:17:56PM +0100, Michael Kerrisk (man-pages) wrote: [..] > >> .BR KEXEC_ON_CRASH " (since Linux 2.6.13)" > >> Execute the new kernel automatically on a system crash. > >> .\" FIXME Explain in more detail how KEXEC_ON_CRASH is actually used > > I wasn't expecting that you would respond to the FIXMEs that were > not labeled "kexec_file_load", but I was hoping you might ;-). Thanks! > I have a few additional questions to your nice notes. > > > Upon boot first kernel reserves a chunk of contiguous memory (if > > crashkernel=<> command line paramter is passed). This memory is > > is used to load the crash kernel (Kernel which will be booted into > > if first kernel crashes). > Hi Michael, > Can I just confirm: is it in all cases only possible to use kexec_load() > and kexec_file_load() if the kernel was booted with the 'crashkernel' > parameter set? As of now, only kexec_load() and kexec_file_load() system calls can make use of memory reserved by crashkernel=<> kernel parameter. And this is used only if we are trying to load a crash kernel (KEXEC_ON_CRASH flag specified). > > > Location of this reserved memory is exported to user space through > > /proc/iomem file. > > Is that export via an entry labeled "Crash kernel" in the > /proc/iomem file? Yes. > > > User space can parse it and prepare list of segments > > specifying this reserved memory as destination. > > I'm not quite clear on "specifying this reserved memory as destination". > Is that done by specifying the address in the kexec_segment.mem fields? You are absolutely right. User space can specify in kexec_segment.mem field the memory location where it expecting a particular segment to be loaded by kernel. > > > Once kernel sees the flag KEXEC_ON_CRASH, it makes sure that all the > > segments are destined for reserved memory otherwise kernel load operation > > fails. > > Could you point me to where this checking is done? Also, what is the > error (errno) that occurs when the load operation fails? (I think the > answers to these questions are "at the start of kimage_alloc_init()" > and "EADDRNOTAVAIL", but I'd like to confirm.) This checking happens in sanity_check_segment_list() which is called by kimage_alloc_init(). And yes, error code returned is -EADDRNOTAVAIL. > > > [..] > >> struct kexec_segment { > >> void *buf; /* Buffer in user space */ > >> size_t bufsz; /* Buffer length in user space */ > >> void *mem; /* Physical address of kernel */ > >> size_t memsz; /* Physical address length */ > >> }; > >> .fi > >> .in > >> .PP > >> .\" FIXME Explain the details of how the kernel image defined by segments > >> .\" is copied from the calling process into previously reserved memory. > > > > Kernel image defined by segments is copied into kernel either in regular > > memory > > Could you clarify what you mean by "regular memory"? I meant memory which is not reserved memory. > > > or in reserved memory (if KEXEC_ON_CRASH is set). Kernel first > > copies list of segments in kernel memory and then goes does various > > sanity checks on the segments. If everything looks line, kernel copies > > segment data to kernel memory. > > > > In case of normal kexec, segment data is loaded in any available memory > > and segment data is moved to final destination at the kexec reboot time. > > By "moved to final destination", do you mean "moved from user space to the > final kernel-space destination"? No. Segment data moves from user space to kernel space once kexec_load() call finishes successfully. But when user does reboot (kexec -e), at that time kernel moves that segment data to its final location. Kernel could not place the segment at its final location during kexec_load() time as that memory is already in use by running kernel. But once we are about to reboot to new kernel, we can overwrite the old kernel's memory. > > > In case of kexec on panic (KEXEC_ON_CRASH flag set), segment data is > > directly loaded to reserved memory and after crash kexec simply jumps > > By "directly", I assume you mean "at the time of the kexec_laod() call", > right? Yes. Thanks Vivek From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: Edited kexec_load(2) [kexec_file_load()] man page for review Date: Mon, 12 Jan 2015 17:16:34 -0500 Message-ID: <20150112221634.GD16162@redhat.com> References: <545FBDDD.9060801@gmail.com> <20141111213037.GA31445@redhat.com> <54ADA284.30502@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <54ADA284.30502-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Michael Kerrisk (man-pages)" Cc: lkml , "linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Andy Lutomirski , Dave Young , "H. Peter Anvin" , Borislav Petkov , "Eric W. Biederman" List-Id: linux-man@vger.kernel.org On Wed, Jan 07, 2015 at 10:17:56PM +0100, Michael Kerrisk (man-pages) wrote: [..] > >> .BR KEXEC_ON_CRASH " (since Linux 2.6.13)" > >> Execute the new kernel automatically on a system crash. > >> .\" FIXME Explain in more detail how KEXEC_ON_CRASH is actually used > > I wasn't expecting that you would respond to the FIXMEs that were > not labeled "kexec_file_load", but I was hoping you might ;-). Thanks! > I have a few additional questions to your nice notes. > > > Upon boot first kernel reserves a chunk of contiguous memory (if > > crashkernel=<> command line paramter is passed). This memory is > > is used to load the crash kernel (Kernel which will be booted into > > if first kernel crashes). > Hi Michael, > Can I just confirm: is it in all cases only possible to use kexec_load() > and kexec_file_load() if the kernel was booted with the 'crashkernel' > parameter set? As of now, only kexec_load() and kexec_file_load() system calls can make use of memory reserved by crashkernel=<> kernel parameter. And this is used only if we are trying to load a crash kernel (KEXEC_ON_CRASH flag specified). > > > Location of this reserved memory is exported to user space through > > /proc/iomem file. > > Is that export via an entry labeled "Crash kernel" in the > /proc/iomem file? Yes. > > > User space can parse it and prepare list of segments > > specifying this reserved memory as destination. > > I'm not quite clear on "specifying this reserved memory as destination". > Is that done by specifying the address in the kexec_segment.mem fields? You are absolutely right. User space can specify in kexec_segment.mem field the memory location where it expecting a particular segment to be loaded by kernel. > > > Once kernel sees the flag KEXEC_ON_CRASH, it makes sure that all the > > segments are destined for reserved memory otherwise kernel load operation > > fails. > > Could you point me to where this checking is done? Also, what is the > error (errno) that occurs when the load operation fails? (I think the > answers to these questions are "at the start of kimage_alloc_init()" > and "EADDRNOTAVAIL", but I'd like to confirm.) This checking happens in sanity_check_segment_list() which is called by kimage_alloc_init(). And yes, error code returned is -EADDRNOTAVAIL. > > > [..] > >> struct kexec_segment { > >> void *buf; /* Buffer in user space */ > >> size_t bufsz; /* Buffer length in user space */ > >> void *mem; /* Physical address of kernel */ > >> size_t memsz; /* Physical address length */ > >> }; > >> .fi > >> .in > >> .PP > >> .\" FIXME Explain the details of how the kernel image defined by segments > >> .\" is copied from the calling process into previously reserved memory. > > > > Kernel image defined by segments is copied into kernel either in regular > > memory > > Could you clarify what you mean by "regular memory"? I meant memory which is not reserved memory. > > > or in reserved memory (if KEXEC_ON_CRASH is set). Kernel first > > copies list of segments in kernel memory and then goes does various > > sanity checks on the segments. If everything looks line, kernel copies > > segment data to kernel memory. > > > > In case of normal kexec, segment data is loaded in any available memory > > and segment data is moved to final destination at the kexec reboot time. > > By "moved to final destination", do you mean "moved from user space to the > final kernel-space destination"? No. Segment data moves from user space to kernel space once kexec_load() call finishes successfully. But when user does reboot (kexec -e), at that time kernel moves that segment data to its final location. Kernel could not place the segment at its final location during kexec_load() time as that memory is already in use by running kernel. But once we are about to reboot to new kernel, we can overwrite the old kernel's memory. > > > In case of kexec on panic (KEXEC_ON_CRASH flag set), segment data is > > directly loaded to reserved memory and after crash kexec simply jumps > > By "directly", I assume you mean "at the time of the kexec_laod() call", > right? Yes. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1YAnIU-000706-3n for kexec@lists.infradead.org; Mon, 12 Jan 2015 22:17:19 +0000 Date: Mon, 12 Jan 2015 17:16:34 -0500 From: Vivek Goyal Subject: Re: Edited kexec_load(2) [kexec_file_load()] man page for review Message-ID: <20150112221634.GD16162@redhat.com> References: <545FBDDD.9060801@gmail.com> <20141111213037.GA31445@redhat.com> <54ADA284.30502@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <54ADA284.30502@gmail.com> 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" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: "Michael Kerrisk (man-pages)" Cc: "linux-man@vger.kernel.org" , kexec@lists.infradead.org, lkml , Andy Lutomirski , Borislav Petkov , "Eric W. Biederman" , "H. Peter Anvin" , Dave Young On Wed, Jan 07, 2015 at 10:17:56PM +0100, Michael Kerrisk (man-pages) wrote: [..] > >> .BR KEXEC_ON_CRASH " (since Linux 2.6.13)" > >> Execute the new kernel automatically on a system crash. > >> .\" FIXME Explain in more detail how KEXEC_ON_CRASH is actually used > > I wasn't expecting that you would respond to the FIXMEs that were > not labeled "kexec_file_load", but I was hoping you might ;-). Thanks! > I have a few additional questions to your nice notes. > > > Upon boot first kernel reserves a chunk of contiguous memory (if > > crashkernel=<> command line paramter is passed). This memory is > > is used to load the crash kernel (Kernel which will be booted into > > if first kernel crashes). > Hi Michael, > Can I just confirm: is it in all cases only possible to use kexec_load() > and kexec_file_load() if the kernel was booted with the 'crashkernel' > parameter set? As of now, only kexec_load() and kexec_file_load() system calls can make use of memory reserved by crashkernel=<> kernel parameter. And this is used only if we are trying to load a crash kernel (KEXEC_ON_CRASH flag specified). > > > Location of this reserved memory is exported to user space through > > /proc/iomem file. > > Is that export via an entry labeled "Crash kernel" in the > /proc/iomem file? Yes. > > > User space can parse it and prepare list of segments > > specifying this reserved memory as destination. > > I'm not quite clear on "specifying this reserved memory as destination". > Is that done by specifying the address in the kexec_segment.mem fields? You are absolutely right. User space can specify in kexec_segment.mem field the memory location where it expecting a particular segment to be loaded by kernel. > > > Once kernel sees the flag KEXEC_ON_CRASH, it makes sure that all the > > segments are destined for reserved memory otherwise kernel load operation > > fails. > > Could you point me to where this checking is done? Also, what is the > error (errno) that occurs when the load operation fails? (I think the > answers to these questions are "at the start of kimage_alloc_init()" > and "EADDRNOTAVAIL", but I'd like to confirm.) This checking happens in sanity_check_segment_list() which is called by kimage_alloc_init(). And yes, error code returned is -EADDRNOTAVAIL. > > > [..] > >> struct kexec_segment { > >> void *buf; /* Buffer in user space */ > >> size_t bufsz; /* Buffer length in user space */ > >> void *mem; /* Physical address of kernel */ > >> size_t memsz; /* Physical address length */ > >> }; > >> .fi > >> .in > >> .PP > >> .\" FIXME Explain the details of how the kernel image defined by segments > >> .\" is copied from the calling process into previously reserved memory. > > > > Kernel image defined by segments is copied into kernel either in regular > > memory > > Could you clarify what you mean by "regular memory"? I meant memory which is not reserved memory. > > > or in reserved memory (if KEXEC_ON_CRASH is set). Kernel first > > copies list of segments in kernel memory and then goes does various > > sanity checks on the segments. If everything looks line, kernel copies > > segment data to kernel memory. > > > > In case of normal kexec, segment data is loaded in any available memory > > and segment data is moved to final destination at the kexec reboot time. > > By "moved to final destination", do you mean "moved from user space to the > final kernel-space destination"? No. Segment data moves from user space to kernel space once kexec_load() call finishes successfully. But when user does reboot (kexec -e), at that time kernel moves that segment data to its final location. Kernel could not place the segment at its final location during kexec_load() time as that memory is already in use by running kernel. But once we are about to reboot to new kernel, we can overwrite the old kernel's memory. > > > In case of kexec on panic (KEXEC_ON_CRASH flag set), segment data is > > directly loaded to reserved memory and after crash kexec simply jumps > > By "directly", I assume you mean "at the time of the kexec_laod() call", > right? Yes. Thanks Vivek _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec