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

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Message-ID: <6950516.1uefDuthAH@hammer82.arch.suse.de>
Date:	Tue, 29 Jan 2013 02:05:53 +0100
From:	Thomas Renninger <trenn@...e.de>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org, vgoyal@...hat.com, horms@...ge.net.au,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/2] x86 e820: Introduce memmap=resetusablemap for kdump usage

On Wednesday, January 23, 2013 08:07:19 PM Yinghai Lu wrote:
> On Tue, Jan 22, 2013 at 12:06 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> > On Tue, Jan 22, 2013 at 8:32 AM, H. Peter Anvin <hpa@...or.com> wrote:
> >>> Again: Please explain what is bad with this solution.
> >>> I cannot see a better and more robust way for kdump other than
> >>> reserving the original reserved memory areas as declared by the BIOS.
> >> 
> >> It is bad because it creates more complexity than is needed.
> >> 
> >> The whole point is that what we want is simply to switch type 1 to type
> >> X, with the sole exceptions being the areas explicitly reserved for the
> >> kdump kernel.
> > 
> > Do you prefer to  "reserveram" way in attached patch?
> 
> Hi, Thomas,
> 
> Can you please check attached reserveram version on your setup?
> 
> If it is ok, i will put it in for-x86-boot patchset and send it to
> Peter for v3.9.

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...

       Thomas
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