Re: [RFD] efi assisted kdump

From: Dave Young <dyoung@redhat.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: matt.fleming@intel.com,
	Kweh Hock Leong <hock.leong.kweh@intel.com>,
	linux-efi@vger.kernel.org, kexec@lists.infradead.org,
	vgoyal@redhat.com
Subject: Re: [RFD] efi assisted kdump
Date: Tue, 27 Jan 2015 14:37:42 +0800	[thread overview]
Message-ID: <20150127063742.GE2506@darkstar.redhat.com> (raw)
In-Reply-To: <20150126163941.GD3320@codeblueprint.co.uk>

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@console-pimps.org
>   https://lkml.kernel.org/r/1414984030-13859-1-git-send-email-hock.leong.kweh@intel.com
> 
> 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

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