Re: Oops in 2.4.0-ac5

[David Woodhouse <dwmw2@infradead.org>]

mingo@redhat.com said:
>  i prefer clear oopses and bug reports instead of ignoring them. A
> failed MSR write is not something to be taken easily. MSR writes if
> fail mean that there is a serious kernel bug - we want to stop the
> kernel and complain ASAP. And correct code will be much more readable
> that way.

The bug here seems to be that we're using the same bit (X86_FEATURE_APIC) to
report two _different_ features. 

We don't represent X86_FEATURE_CXMMX and X86_FEATURE_MMX with the same bit, 
even though they are supposed to provide the same functionality - because 
they are in fact different. Likewise we shouldn't use the same bit for the 
two different types of APIC, IMO.

Index: include/asm-i386/cpufeature.h
===================================================================
RCS file: /inst/cvs/linux/include/asm-i386/Attic/cpufeature.h,v
retrieving revision 1.1.2.1
diff -u -r1.1.2.1 cpufeature.h
--- include/asm-i386/cpufeature.h	2000/12/05 13:30:46	1.1.2.1
+++ include/asm-i386/cpufeature.h	2001/01/11 11:12:41
@@ -62,6 +62,7 @@
 #define X86_FEATURE_K6_MTRR	(3*32+ 1) /* AMD K6 nonstandard MTRRs */
 #define X86_FEATURE_CYRIX_ARR	(3*32+ 2) /* Cyrix ARRs (= MTRRs) */
 #define X86_FEATURE_CENTAUR_MCR	(3*32+ 3) /* Centaur MCRs (= MTRRs) */
+#define X86_FEATURE_AMD_APIC	(3*32+ 4) /* AMD Athlon CPU-local APIC */
 
 #endif /* __ASM_I386_CPUFEATURE_H */
 
Index: arch/i386/kernel/setup.c
===================================================================
RCS file: /inst/cvs/linux/arch/i386/kernel/setup.c,v
retrieving revision 1.4.2.47
diff -u -r1.4.2.47 setup.c
--- arch/i386/kernel/setup.c	2001/01/01 12:56:13	1.4.2.47
+++ arch/i386/kernel/setup.c	2001/01/11 11:12:41
@@ -1058,6 +1058,11 @@
 			break;
 
 		case 6:	/* An Athlon/Duron. We can trust the BIOS probably */
+			if (test_bit(X86_FEATURE_APIC, &c->x86_capability)) {
+				/* Not a compatible APIC */
+				clear_bit(X86_FEATURE_APIC, &c->x86_capability);
+				set_bit(X86_FEATURE_AMD_APIC, &c->x86_capability);
+			}
 			break;		
 	}
 

--
dwmw2


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