From: "Segher Boessenkool" <segher@kernel•crashing.org>
To: "Albert Cahalan" <acahalan@gmail•com>
Cc: linuxppc-dev@lists•ozlabs.org
Subject: Re: use of BAT before taking over the MMU
Date: Mon, 4 Oct 2010 06:25:25 +0200 (CEST) [thread overview]
Message-ID: <63799.84.105.60.153.1286166325.squirrel@gate.crashing.org> (raw)
In-Reply-To: <AANLkTikPhpvJetY+NDFggYE6Wp6ppyt2BLmzEbsiwHuZ@mail.gmail.com>
> On the prom boot path, with the firmware supposed to
> be managing the MMU, there is a case where:
>
> 1. Linux changes some BAT registers.
> 2. Bits 0x00000070 are/become set in the MSR.
> 3. Linux takes an MMU fault.
> 4. The firmware handles it.
>
> AFAIK, you can't expect the firmware to leave the BAT alone.
> If the firmware provides mapping services by using the BAT
> as a software-filled TLB, Linux's BAT changes may be lost.
>
> You also can't expect that your BAT changes will not conflict
> with mappings that the firmware uses for itself. The firmware
> might write to your new BAT mapping, relying on those virtual
> addresses to be something else entirely.
The PowerPC OF binding requires the firmware to save and restore
the BATs on entry to / exit from the firmware.
Segher
next prev parent reply other threads:[~2010-10-04 4:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-02 18:32 use of BAT before taking over the MMU Albert Cahalan
2010-10-04 4:25 ` Segher Boessenkool [this message]
2010-10-04 16:06 ` Albert Cahalan
2010-10-05 7:54 ` Segher Boessenkool
2010-10-05 8:11 ` Benjamin Herrenschmidt
2010-10-05 8:10 ` Benjamin Herrenschmidt
2010-10-05 12:05 ` Albert Cahalan
2010-10-05 12:28 ` Benjamin Herrenschmidt
2010-10-05 15:31 ` Segher Boessenkool
2010-10-07 2:05 ` Albert Cahalan
2010-10-07 8:00 ` Benjamin Herrenschmidt
2010-10-05 15:22 ` Segher Boessenkool
2010-10-05 8:09 ` Benjamin Herrenschmidt
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