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Date: Mon, 8 Dec 1997 14:00:02 -0800 (PST)
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From: Steve Passe <smp@csn.net>
Subject: Re: kern/5244: F00F workaround dosn't always work on SMP system. 
Reply-To: Steve Passe <smp@csn.net>
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The following reply was made to PR kern/5244; it has been noted by GNATS.

From: Steve Passe <smp@csn.net>
To: freebsd-gnats-submit@FreeBSD.ORG
Cc: mgove@cais.com, smp@FreeBSD.ORG
Subject: Re: kern/5244: F00F workaround dosn't always work on SMP system. 
Date: Mon, 08 Dec 1997 14:53:21 -0700

 Hi,
 
 > >Number:         5244
 > >Category:       kern
 > >Synopsis:       F00F workaround dosn't always work on SMP system.
 > > ...
 > >Description:
 > Intel F00F workaround appears to only install on the first CPU in a dual CPU configuration.
 > 
 > >How-To-Repeat:
 > Execute the 'F00F' code, repeatedly.  Sometimes it dies with Illegal instruction, sometimes the system hangs.
 > 
 
 The basic problem is the fact that r_idt is local in UP, and global in SMP.
 This is because SMP:init_secondary() uses the global r_idt to sync the
 additional CPUs to the boot CPU:
 
 ---
 machdep.c:
 
  ...
 
 #ifdef SMP
 /* table descriptors - used to load tables by microp */
 struct region_descriptor r_gdt, r_idt;
 #endif
 
  ...
 
 init386(first)
 	int first;
 {
  ...
 #ifndef SMP
 	/* table descriptors - used to load tables by microp */
 	struct region_descriptor r_gdt, r_idt;
 #endif
 
 ---
 mp_machdep.c:
 
 init_secondary(void)
 {
  ...
 	lidt(&r_idt);
 	lldt(_default_ldt);
 
 ---
 I think to trick is to rework f00f_hack() to use the global in the SMP case,
 AND to insure that init_secondary() runs AFTER f00f_hack().
 
 I'm not clear on what f00f_hack() does, and do not have the available
 hardware to test it (ie dual P5), so I'll have to leave this to someone
 else to deal with...
 
 --
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