linux-kernel - Re: [PATCH 2/2] x86 e820: Introduce memmap=resetusablemap for kdump usage

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Message-ID: <510721C6.6080705@zytor.com>
Date:	Mon, 28 Jan 2013 17:11:34 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Renninger <trenn@...e.de>
CC:	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	vgoyal@...hat.com, horms@...ge.net.au
Subject: Re: [PATCH 2/2] x86 e820: Introduce memmap=resetusablemap for kdump
 usage

On 01/28/2013 05:05 PM, Thomas Renninger wrote:
> 
> But this (converting usable memory to reserved one before usable kdump memory
> is added) will let machines run into problems again for which the check:
> "mmconf area must be in reserved memory" got added?
> 
> If, then memory which was usable before has to be converted to a special
> E820_KUMP (or whatever type) to make sure existing checks which look for
> "is reserved memory" still work the same way as in a productive kernel.
> 
> Advantage of this would be that the info what originally was usable
> memory is preserved and can be used in future kdump related patches.
> 
> So I guess the final patch should be:
>    - Add a new e820 type:
>         E820_KDUMP_RESERVED /* Originally usable memory where the crashed
>                                                     kernel kernel resided in */
>   - Use Yinghai's last posted patch, but instead of:
> +			e820_update_range(0, ULLONG_MAX, E820_RAM,
> +					  E820_RESERVED);
> ...
> +			e820_remove_range(start_at, mem_size, E820_RESERVED, 0);
> do:
> +			e820_update_range(0, ULLONG_MAX, E820_RAM,
> +					  E820_KDUMP_RESERVED);
> ...
> +			e820_remove_range(start_at, mem_size, E820_KDUMP_RESERVED, 0);
> 
>   - Come up with another memmap=kdump_reserve_ram memmap option name
>     or however it should get named...
> 
> If this proposal gets accepted, I can send a tested patch...
> 

Yes, this is much saner.  There really shouldn't need to be an option,
even; since the tools need to be modified anyway, just modify the actual
memory map data structure itself.

	-hpa


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