Re: [RFD] efi assisted kdump

[Dave Young <dyoung-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 01/26/15 at 09:08am, Vivek Goyal wrote:
> On Sat, Jan 24, 2015 at 09:26:37PM +0800, Dave Young wrote:
> > Hi,
> > 
> > Kdump has several limitations currently such as kdump kernel reboot will bypass
> > device shutdown path so device drivers should reset during initialization.
> > 
> > * One of such problem we encounter now is the iommu
> > issue, 1st kernel's on fly DMA requests cause 2nd kernel hang. There's some effort
> > on this area, Zhenhua Li posted patches to resolve the intel iommu issue which is
> > under review. But that is just one case there's other possible problems in the future.
> > 
> > * There's no serial console on most machines in the market especially for desktop
> > machines and laptops. kms enabled kernel need drm layer driver for framebuffer
> > console, after kernel crashing we need a console to see the 2nd kernel output
> > ideally a serial console because we can not switch back to VGA mode.
> > 
> > ppc64 has a feature "firmware assisted kdump", see below documentation:
> > Documentation/powerpc/firmware-assisted-dump.txt
> > 
> > In case UEFI machines I wonder if we can do similar things, basic idea is doing
> > minimum thing based on original kdump process.
> > 
> > kernel reserve crashkernel memory during early boot
> >  -> user (kdump service) save necessary informations in some way so that second
> >     kernel boot can access ie. efi runtime variables or in reserved memory
> >     * crashkernel memory ranges infomation
> >     * collect infomations and save elf notes for 2nd kernel vmcore initialization
> 
> I think anything related to vmcore initilization can be in memory
> somewhere and should not be a problem.
> 
> But we do have to think about anything which is passed in bootparams or
> command line to second kenrnel with current mechanism, how will it be
> passed to second kernel.

Hi, Vivek,

Since we are rebooting via efi maybe we can just choose another boot entry
in grub.cfg with the proper cmdline?

Thanks
Dave