From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Young Subject: Re: [RFD] efi assisted kdump Date: Tue, 27 Jan 2015 14:37:42 +0800 Message-ID: <20150127063742.GE2506@darkstar.redhat.com> References: <20150124132637.GB2139@darkstar.redhat.com> <20150126163941.GD3320@codeblueprint.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150126163941.GD3320-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Matt Fleming Cc: Kweh Hock Leong , linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, matt.fleming-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org List-Id: linux-efi@vger.kernel.org Hi, Matt Thanks for the feedback. On 01/26/15 at 04:39pm, Matt Fleming wrote: > On Sat, 24 Jan, at 09:26:37PM, Dave Young wrote: > > > > There's several things I need to ask for help from EFI gurus to see if it is doable: > > > > * Make sure in case EFI warm reboot the memory of previous kernel can be retained. > > The only way to reserve memory across a reboot is with EFI capsules. I know your capsules patchset, but I did not look into the details. Do you means the old memory will be not reliable in case booting without capsules even for warm reboot? > > > * How to determine if kernel is boot with EFI warm reboot in stub > > The presence of a capsule would indicate whether we were invoked from a > crash handler. Ok, another problem is for efi capsule handling, can we do it in efi stub, or I in a efi application, which stage is the doable? > > > * What is the right way to pass informations from 1st kernel to 2nd kernel. > > Is it ok for saving something with efi variables? > > EFI capsules would the be most natural mechanism, but you could > conceivably do it with EFI variables (there's an upper limit on the size > of variable data, though). Will think about it after I checking the capsule machanisms details. > > > * Other possible problems what I missed > > Support for runtime EFI capsules was rather spotty last time I looked. > Things may have moved on, but it's definitely something to watch out > for. > > There have been patches on linux-efi in recent months for making use of > EFI capsules, > > https://lkml.kernel.org/r/1412692886-25306-1-git-send-email-matt-HNK1S37rvNbeXh+fF434Mdi2O/JbrIOy@public.gmane.org > https://lkml.kernel.org/r/1414984030-13859-1-git-send-email-hock.leong.kweh-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org > > I could take a look at resubmitting the first series above if that would > be useful for doing kexec across a reset. Thanks a lot. I will take a look at how capsules works firstly. Dave