Date:   Sun, 9 Apr 2000 14:03:54 +0200
From:   "Andi Kleen" <ak@suse.de>
To:     suzukis@file.phys.tohoku.ac.jp
Cc:     linux-xfs@oss.sgi.com
Subject: Re: 486 and Linux-2.3.99pre2+XFS
Message-ID: <20000409140354.A29535@gruyere.muc.suse.de>
References: <20000409100802.10137.qmail@file.phys.tohoku.ac.jp>
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In-Reply-To: <20000409100802.10137.qmail@file.phys.tohoku.ac.jp>; from suzukis@file.phys.tohoku.ac.jp on Sun, Apr 09, 2000 at 07:08:02PM +0900
Sender: owner-linux-xfs@oss.sgi.com
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On Sun, Apr 09, 2000 at 07:08:02PM +0900, suzukis@file.phys.tohoku.ac.jp wrote:
> # For first, I must apologize,
> # this is NOT related to the XFS implementation itself,
> # this is related to the kernel source publisized by SGI.
> # However, I wish, it's not completely-meaningless for
> # linux-xfs subscribers who failed to run on 486 PC.
> 
> Hello,
> 
> There's anybody who makes Linux-XFS kernel (by SGI)
> running on 486 PC? Yet I've not succeed to do it.
> Even if the kernel can run on 586 (and later) PCs,
> it fails on 486. Of course, I choose 386 + math emulation
> in kernel configuration. I receive following message.

This is a KDB bug. It uses Pentium specific MSRs without checking that it
really runs on a Pentium. Try turning off CONFIG_KDB or apply the following
patch: 

-Andi

--- linux/arch/i386/kdb/kdbasupport.c-k6kdb	Sat Mar 25 01:41:33 2000
+++ linux/arch/i386/kdb/kdbasupport.c	Mon Apr  3 20:50:59 2000
@@ -37,6 +37,41 @@
 unsigned long smp_kdb_wait;
 #endif
 
+enum cpu { IntelP5, IntelP6, AmdK6, Unknown } kdba_msrtype; 
+
+/* The normal kernel does the same, but be independent. */ 
+static void 
+kdba_checkcpu(void) 
+{ 
+	union { 
+		char str[12]; 
+		__u32 reg[3];  
+	} v; 
+	int eax,ebx,ecx,edx; 
+	__asm__("cpuid" 
+		: "=a" (eax), "=b" (v.reg[0]) , "=c" (v.reg[1]), "=d" (v.reg[2])
+		: "a" (0)); 
+	__asm__("cpuid"
+		: "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx)
+		: "a" (1)); 
+
+	kdba_msrtype = Unknown; 
+	if (!strcmp(v.str, "GenuineIntel")) {
+		switch ((ebx >> 4) & 0xF) { 
+		case 5:
+			kdba_msrtype = IntelP5;
+			break;
+		case 6:
+			kdba_msrtype = IntelP6;
+			break;
+		}			
+	} else if (!strcmp(v.str, "AuthenticAMD") && (((ebx >> 4) & 0xF) == 6)) {
+		kdba_msrtype = AmdK6; 
+	}
+} 
+
+
+
 void
 kdba_installdbreg(kdb_bp_t *bp)
 {
@@ -708,6 +743,11 @@
 {
 	u32  lv, hv;
 
+	if (kdba_msrtype != IntelP6) { 
+		kdb_printf("Last branch information not supported on this CPU.\n");
+		return;
+	}
+
 	rdmsr(DEBUGCTLMSR, lv, hv);
 	lv |= 0x1;	/* Set LBR enable */
 	wrmsr(DEBUGCTLMSR, lv, hv);
@@ -734,6 +774,11 @@
 	u32  bflv, bfhv;
 	u32  btlv, bthv;
 
+	if (kdba_msrtype != IntelP6) { 
+		kdb_printf("Last branch information not supported on this CPU.\n");
+		return;
+	}
+
 	rdmsr(LASTBRANCHFROMIP, bflv, bfhv);
 	rdmsr(LASTBRANCHTOIP, btlv, bthv);
 	kdb_printf("Last Branch IP, from: 0x%x  to 0x%x\n",
@@ -1087,6 +1132,7 @@
 void
 kdba_init(void)
 {
+	kdba_checkcpu(); 
 	kdba_enablelbr();
 
 	return;
--- linux/arch/i386/kernel/entry.S-k6kdb	Sat Mar 25 01:41:33 2000
+++ linux/arch/i386/kernel/entry.S	Mon Apr  3 20:52:24 2000
@@ -432,16 +432,6 @@
 	jmp error_code
 
 ENTRY(page_fault)
-	pushl %ecx
-	pushl %edx
-	pushl %eax
-	movl  $473,%ecx
-	rdmsr
-	andl  $0xfffffffe,%eax
-	wrmsr
-	popl  %eax
-	popl  %edx
-	popl  %ecx
 	pushl $ SYMBOL_NAME(do_page_fault)
 	jmp error_code