Message-ID: <F2DBA543B89AD51184B600508B68D4000F866009@fmsmsx103.fm.intel.com>
From: "Nakajima, Jun" <jun.nakajima@intel.com>
To: torvalds@transmeta.com
Cc: linux-kernel@vger.kernel.org
Subject: RE: local APIC may cause XFree86 hang
Date: Wed, 13 Nov 2002 16:29:48 -0800
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Are we disabling vm86 code to access to PIT or PIC? I saw some video ROM
code (either BIOS call or far call) did access PIT, confusing the OS.

Thanks,
Jun

> -----Original Message-----
> From: torvalds@transmeta.com [mailto:torvalds@transmeta.com]
> Sent: Wednesday, November 13, 2002 3:53 PM
> To: linux-kernel@vger.kernel.org
> Subject: Re: local APIC may cause XFree86 hang
> 
> In article <15826.53818.621879.661253@kim.it.uu.se>,
> Mikael Pettersson  <mikpe@csd.uu.se> wrote:
> >
> >Does XFree86 (its core or particular drivers) use vm86() to
> >invoke, possibly graphics card specific, BIOS code?
> >That would explain the hangs I got. The fix would be to
> >disable the local APIC around vm86()'s BIOS calls, just like
> >we now disable it before APM suspend.
> 
> It does.
> 
> HOWEVER, vm86() mode is very very different from APM, which uses real
> mode.  External interrupts in vm86 mode will not be taken inside vm86
> mode - and disabling the local timer (by disabling the APIC) around a
> vm86 mode is definitely _not_ a good idea, since it would be an instant
> denial-of-service attack on SMP machines (the PIT timer only goes to
> CPU0, so we depend on the local timer to do process timeouts etc on
> other CPUs).  The vm86 code might just be looping forever.
> 
> In other words, if it is really vm86-related, then
>  (a) it's a CPU bug
>  (b) we're screwed
> 
> I bet it's something else.  Possibly just timing-specific (the APIC
> makes interrupts much faster), but also possibly something to do with
> the VGA interrupt (some XFree86 drivers actually use the gfx interrupts
> these days)
> 
> 		Linus
> -
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