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From: "H. Peter Anvin" <hpa@zytor.com>
To: "Ahmed S. Darwish" <darwish.07@gmail.com>
Cc: 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>
Subject: Re: [PATCH -next 1/2][RFC] x86: Saveoops: Switch to real-mode and call	BIOS
Date: Tue, 25 Jan 2011 09:26:18 -0800	[thread overview]
Message-ID: <4D3F07BA.5030702@zytor.com> (raw)
In-Reply-To: <20110125135122.GB10051@laptop>

On 01/25/2011 05:51 AM, Ahmed S. Darwish wrote:
> 
> We get called here upon panic()s to save the kernel log buffer.
> 
> First, switch from 64-bit long mode to 16-bit real mode. Afterwards, save the
> log buffer to disk using extended INT 0x13 BIOS services. The user has given
> us an absolute LBA disk address to save the log buffer to.
> 
> By x86 design, this code is mandated to run on a single identity-mapped page.
> 
> - How to initialize the disk hardware to its POST state (thus making the
>   BIOS code work reliably) while keeping system RAM unmodified?

You can't safely do so, really.

> - Is it guaranteed that '0x80' will always be the boot disk drive number?
>   If not, we need to be passed the boot drive number from the bootloader.

It's not, and we may not even be booting from disk.

This code seems extremely dangerous, in the "may eat your data" kind of
way.  Using the BIOS once the kernel has run is cantankerous, using it
to *write* is potentially lethal.

	-hpa



  reply	other threads:[~2011-01-25 17:29 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-25 13:47 [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic Ahmed S. Darwish
2011-01-25 13:51 ` [PATCH -next 1/2][RFC] x86: Saveoops: Switch to real-mode and call BIOS Ahmed S. Darwish
2011-01-25 17:26   ` H. Peter Anvin [this message]
2011-01-25 13:53 ` [PATCH -next 2/2][RFC] x86: Saveoops: Reserve low memory and register code Ahmed S. Darwish
2011-01-25 17:29   ` H. Peter Anvin
2011-01-26  9:04     ` Ahmed S. Darwish
2011-01-25 14:09 ` [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic Ingo Molnar
2011-01-25 15:08   ` Tejun Heo
2011-01-25 17:33     ` H. Peter Anvin
2011-01-26 11:44       ` Ahmed S. Darwish
2011-02-03 14:36     ` Pavel Machek
2011-02-03 15:28       ` H. Peter Anvin
2011-02-03 17:57         ` Ingo Molnar
2011-02-03 21:07           ` H. Peter Anvin
2011-01-25 15:36   ` Ahmed S. Darwish
2011-01-25 16:02     ` James Bottomley
2011-01-25 17:05       ` Ahmed S. Darwish
2011-01-25 17:20         ` James Bottomley
2011-01-25 22:10         ` Mark Lord
2011-01-25 22:16           ` Randy Dunlap
2011-01-25 22:45             ` Jeff Garzik
2011-01-25 22:58               ` H. Peter Anvin
2011-01-26  0:26                 ` Jeff Garzik
2011-01-31  2:59                 ` Rusty Russell
2011-01-31 10:45                   ` Ingo Molnar
2011-01-25 17:32     ` Tony Luck
2011-01-25 17:36       ` H. Peter Anvin
2011-01-25 19:04       ` Jeff Garzik
2011-01-25 14:49 ` Tejun Heo
2011-01-28  7:59   ` Jan Ceuleers
2011-01-25 20:25 ` Linus Torvalds
     [not found]   ` <20110126124954.GC24527@laptop>
2011-01-26 23:07     ` Luck, Tony
     [not found]       ` <20110126231620.GA14807@redhat.com>
     [not found]         ` <987664A83D2D224EAE907B061CE93D53019438EB02@orsmsx505.amr.corp.intel.com>
     [not found]           ` <20110126233033.GB14807@redhat.com>
     [not found]             ` <987664A83D2D224EAE907B061CE93D53019438EBB6@orsmsx505.amr.corp.intel.com>
     [not found]               ` <4D40F7F1.3020509@zytor.com>
     [not found]                 ` <20110127120039.GD20279@elte.hu>
2011-01-27 18:35                   ` Luck, Tony
     [not found]                   ` <4D4197CB.9070201@zytor.com>
     [not found]                     ` <20110127162429.GB26437@elte.hu>
2011-01-27 18:56                       ` Luck, Tony
     [not found]     ` <20110127021338.GA20334@redhat.com>
     [not found]       ` <4D40F81E.1030009@zytor.com>
     [not found]         ` <20110127052639.GA16289@laptop>
     [not found]           ` <m1sjweyeax.fsf@fess.ebiederm.org>
2011-02-02 11:13             ` Ahmed S. Darwish

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