On Mon, May 02, 2016 at 01:04:28PM +0530, Pratyush Anand wrote: > On Sat, Apr 30, 2016 at 1:50 PM, Russell King - ARM Linux > <linux at arm.linux.org.uk> wrote: > > On Sat, Apr 30, 2016 at 08:57:34AM +0530, Pratyush Anand wrote: > >> On Fri, Apr 29, 2016 at 11:30 PM, Russell King - ARM Linux > >> <linux at arm.linux.org.uk> wrote: > >> > On Fri, Apr 29, 2016 at 08:26:00PM +0530, Pratyush Anand wrote: > >> >> Hi Russell, > >> >> > >> >> On Thu, Apr 28, 2016 at 2:58 PM, Russell King > >> >> <rmk+kernel at arm.linux.org.uk> wrote: > >> >> > Advertise the location of bootable RAM to kexec-tools. kexec needs to > >> >> > know where it can place the kernel in RAM, and so be executable when > >> >> > the system needs to jump into it. > >> >> > > >> >> > Advertise these areas in /proc/iomem with a "System RAM (boot alias)" > >> >> > tag. > >> >> > > >> >> > Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk> > >> >> > >> >> Can you please also share git tree path of corresponding kexec-tools changes? > >> >> > >> >> Could it be a better idea (if things in user space become simpler) > >> >> that in stead of patch 5 and 6, we pass arch_phys_to_idmap_offset to > >> >> user space, and then user space manipulates existing "Crash kernel" > >> >> and "System RAM" resources. > >> > > >> > Given that it's only _one_ platform right now, I don't think that > >> > additional complexity is worth it. It means that we have to invent > >> > >> Probably, I could not communicate it well. I was not trying to have > >> *additional* complexity. Wanted to see if things could be simpler > >> rather. So this is what my understanding was: > >> -- We create one patch to pass arch_phys_to_idmap_offset to user space > >> (say in /sys/kernel/bootmem_idmap_offset) > >> -- We do not use patch 5,6,11 and 12 of this series. Probably few more > >> content of the series will go away. > > > > Patches 11 and 12 don't go away with what you're suggesting. Patches > > 11 and 12 are necessary to allow the boot-view addresses to be passed > > into the kernel through kexec, and to allow kexec to find appropriate > > memory resources. > > But once we would have manipulated "start" and "end" of "Crash Kernel" > and "System RAM" resources in user space using > /sys/kernel/bootmem_idmap_offset , then kernel through kexec system > call would have already receive boot-view addresses, no? Correct, but that's still a problem for all the reasons I gave in the email to which you replied to. I'm not sure where the misunderstanding is. Let me repeat: even if we do what you're suggesting, patches 11 and 12 do *not* go away. I've explained in detail why each of the changes are necessary (which you have cut from your reply.) In other words: exporting this offset via /sys/kernel/bootmem_idmap_offset is technically inferior to the solution I have come up with here, and it saves very little complexity and code. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
