Messages in this thread | | | Date | Tue, 5 Aug 2008 14:15:56 +0200 | From | Pavel Machek <> | Subject | Re: [patch 20/62] x86, suspend, acpi: enter Big Real Mode |
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On Wed 2008-07-30 16:58:31, Greg KH wrote: > 2.6.26 -stable review patch. If anyone has any objections, please let > us know. > > ------------------ > From: H. Peter Anvin <hpa@zytor.com> > > Commit 3bf2e77453a87c22eb57ed4926760ac131c84459 upstream > > x86, suspend, acpi: enter Big Real Mode > > The explanation for recent video BIOS suspend quirk failures is that > the VESA BIOS expects to be entered in Big Real Mode (*.limit = 0xffffffff) > instead of ordinary Real Mode (*.limit = 0xffff). > > This patch changes the segment descriptors to Big Real Mode instead. > > The segment descriptor registers (what Intel calls "segment cache") is > always active. The only thing that changes based on CR0.PE is how it is > *loaded* and the interpretation of the CS flags. > > The segment descriptor registers contain of the following sub-registers: > selector (the "visible" part), base, limit and flags. In protected mode > or long mode, they are loaded from descriptors (or fs.base or gs.base can > be manipulated directly in long mode.) In real mode, the only thing > changed by a segment register load is the selector and the base, where the > base <- selector << 4. In particular, *the limit and the flags are not > changed*. > > As far as the handling of the CS flags: a code segment cannot be writable > in protected mode, whereas it is "just another segment" in real mode, so > there is some kind of quirk that kicks in for this when CR0.PE <- 0. I'm > not sure if this is accomplished by actually changing the cs.flags register > or just changing the interpretation; it might be something that is > CPU-specific. In particular, the Transmeta CPUs had an explicit "CS is > writable if you're in real mode" override, so even if you had loaded CS > with an execute-only segment it'd be writable (but not readable!) on return > to real mode. I'm not at all sure if that is how other CPUs behave. > > Signed-off-by: "H. Peter Anvin" <hpa@zytor.com> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
ACK.
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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