linux-kernel - Re: [PATCH] x86 e820: only void usable memory areas in memmap=exactmap case

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Message-ID: <CAE9FiQV+W21WcZuuWJYJKXhN4sf0mi=iAFgjX644c3EytPXptw@mail.gmail.com>
Date:	Sun, 13 Jan 2013 18:43:46 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Thomas Renninger <trenn@...e.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	MUNEDA Takahiro <muneda.takahiro@...fujitsu.com>,
	Takao Indoh <indou.takao@...fujitsu.com>,
	linux-pci@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	tokunaga.keiich@...fujitsu.com, kexec@...ts.infradead.org,
	hbabu@...ibm.com, mingo@...hat.com, ddutile@...hat.com,
	vgoyal@...hat.com, ishii.hironobu@...fujitsu.com,
	bhelgaas@...gle.com, tglx@...utronix.de, khalid@...ehiking.org,
	horms@...ge.net.au
Subject: Re: [PATCH] x86 e820: only void usable memory areas in
 memmap=exactmap case

On Sun, Jan 13, 2013 at 6:08 PM, Thomas Renninger <trenn@...e.de> wrote:
> On Saturday, January 12, 2013 09:07:12 AM Yinghai Lu wrote:
>> On Sat, Jan 12, 2013 at 3:31 AM, Thomas Renninger <trenn@...e.de> wrote:
>> >         memmap=exactmap [KNL,X86] Enable setting of an exact
>> >
>> > -                       E820 memory map, as specified by the user.
>> > -                       Such memmap=exactmap lines can be constructed
>> > based on -                       BIOS output or other requirements. See
>> > the memmap=nn@ss -                       option description.
>> > +                       E820 usable memory map, as specified by the user.
>> > +                       All unusable (reserved, ACPI, NVS,...) ranges from
>> > the +                       original e820 table are preserved.
>> > +                       But the usable memory regions from the original
>> > e820 +                       table are removed.
>> > +                       This parameter is explicitly for kdump usage:
>> > +                       The memory the kdump kernel is allowed to use must
>> > +                       be passed via below memmap=nn[KMG]@ss[KMG] param.
>> > +                       All reserved regions the kernel may use for
>> > ioremapping +                       and similar are still considered.
>> > +
>> > +       memmap=voidmap  [KNL,X86] Do not use any e820 ranges from BIOS or
>> > +                       bootloader. Instead you have to pass regions via
>> > +                       below memmap= options.
>>
>> I would suggest to keep memmap=exactmap meaning not changed, and add
>> memmap=exactusablemap
>> instead.
> I disagree.
> I would like to change memmap=exactmap behavior.
>
> Why:
> 1)
> This is a sever bug (for kdump/kexec). I could imagine quite a lot
> kdump related bugs get silently solved by this fix.
> I expect we agree that the change, however it looks like in the end, should
> still get in in this kernel round?
> With my approach, I would also suggest to spread this to stable kernels.
> -> No need to update/patch kexec-tools, things will just work as they should.
>
> 2)
> I would introduce 2 new memmap= options. However they look like, for example:
> =void_usable_map
> =void_orig_map
> and deprecated exactmap= via
> printk(KERN_INFO "exactmap usage changed and is deprecated\n");
> but still fix it.
> Latest kexec-tools will just use memmap=void_usable_map, old ones
> are still fixed via stable kernel updates.

everyone could understand it straightforward:
exactmap:  memmap will be specified, and it should be honored without
considering old any memmap.
exactusablemap: will make sure only old ram range get removed, and
specified usable ranges will become final usable
ranges in the final memmap. so we need to remove overlapping to old
reserved ranges.

aka: exact means EXACT ...

>
>
>> kexec-tools could be updated to support exactusablemap with
>> kernelversion checking for kdump.
> No, please not. It will be a maintenance/compatibility issue that will remain
> for years or ever in kdump and/or the kernel and it's not necessary.

I don't see there is any problem with it.

those just some kind of improvement without considering kdump.
because kdump/scripts already does good job to provide right exactmap
with usable and acpi reserved areas.
for mmconf, some system that range reserved in e820, and some have that in ACPI.
and those systems will have that mmconf enabled in kdumped kernel.

attached is what I like to have with exactusablemap, but maybe is not
needed, and we can just stay with exactmap...

ps: we don't need to add e820_remove_type...

Yinghai

Download attachment "e820_exactusablemap.patch" of type "application/octet-stream" (1819 bytes)