Re: [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic

From: "Ahmed S. Darwish" <darwish.07@gmail.com>
To: James Bottomley <James.Bottomley@suse.de>
Cc: "Tejun Heo" <tj@kernel.org>, "Ingo Molnar" <mingo@elte.hu>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>, X86-ML <x86@kernel.org>,
	"Tony Luck" <tony.luck@intel.com>,
	"Dave Jones" <davej@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Randy Dunlap" <rdunlap@xenotime.net>,
	"Willy Tarreau" <wtarreau@hera.kernel.org>,
	"Willy Tarreau" <w@1wt.eu>,
	"Dirk Hohndel" <hohndel@infradead.org>,
	Dirk.Hohndel@intel.com, IDE-ML <linux-ide@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Peter Zijlstra" <a.p.zijlstra@chello.nl>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Arjan van de Ven" <arjan@infradead.org>,
	"Jeff Garzik" <jgarzik@pobox.com>
Subject: Re: [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic
Date: Tue, 25 Jan 2011 19:05:22 +0200	[thread overview]
Message-ID: <20110125170522.GA16285@laptop> (raw)
In-Reply-To: <1295971355.4955.104.camel@mulgrave.site>

Hi!

On Tue, Jan 25, 2011 at 11:02:35AM -0500, James Bottomley wrote:
> On Tue, 2011-01-25 at 17:36 +0200, Ahmed S. Darwish wrote:
> > The complete __roadblock__ I'm currently facing though is restoring the disk
> > controllers to the state originally setup by the BIOS Power-on self-test (POST).
> > I hope such re-initialization is even technically feasible.
> > 
> > Without such re-initialization, we'll just be risking the BIOS code exploding.
> > That was the case in the 5-minute hang described in the cover sheet (PATCH #0).
> 
> So this is the bit that's not really technically feasible.  BIOS tends
> to run storage devices in a very primitive way (so it takes basic
> settings, for example and sets the device up for one particular channel
> of access).  When preparing the device for an operating system, we have
> to blow away all the bios stuff and put it into a more generally
> performant mode (this isn't just the storage per se, it's also the
> interrupt and routing).  Unfortunately, currently, we don't bother to
> save the settings the BIOS was using, so there's no way to reinitialise
> the device back to bios without an effective reboot.
>

My current x86 laptop includes the very common ATA PIIX controller. If I
dumped the PIC, IOAPIC, and disk controller state in a register file in a
safe area, and re-initialized these before giving control to the BIOS, can
this move the solution space from being not really technically feasible to
"quite possible"?

I have to admit that my knowledge of disk controllers is nil. The final
result though can really be worth the effort (as stated by Ingo's mail),
so I'm _willing_ to explore and prototype different paths.

>
> Most BIOS doesn't seem to contain storage re-POST code that's usable
> (it's all embedded in the boot sequence).
>

There's this arcane `Warm boot with partial re-initialization' BIOS feature
using the CMOS register 0xf, but I don't want to to depend on it either.

> James
> 

Thanks,

-- 
Darwish
http://darwish.07.googlepages.com