Date: Sat, 22 Nov 1997 19:03:16 +0900 From: ohki@gssm.otsuka.tsukuba.ac.jp To: freebsd-bugs@FreeBSD.org Cc: ohki@gssm.otsuka.tsukuba.ac.jp Subject: Pentium f00f problem -- possible fix Message-ID: <199711221003.TAA22516@smr00.gssm.otsuka.tsukuba.ac.jp>
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Hi FreeBSD folks
You might have fixed the problem of newly discovered bug of Pentium.
(code sequence of 0xf0 0x0f 0xc7 0xc8 freezes the system)
I implemented the recommended solution comes from Intel,
and enclosed context diffs.
It is my pleasure if it helps you.
--- locore.s-ORIG Sat Feb 1 21:10:54 1997
+++ locore.s Sat Nov 22 16:42:23 1997
@@ -99,6 +99,17 @@
*/
.data
ALIGN_DATA /* just to be sure */
+#if defined(I586_CPU)
+ /*
+ * work around for f00f problem of Pentium
+ * trap to page fault before the machine hangs
+ */
+ .globl _idt
+ .space PAGE_SIZE - 8*7
+_idt:
+ .space 8*7 /* cause page fault for idt[0] to idt[6] */
+ .space PAGE_SIZE
+#endif defined(I586_CPU)
.globl tmpstk
.space 0x2000 /* space for tmpstk - temporary stack */
--- machdep.c-ORIG Thu Apr 3 15:37:31 1997
+++ machdep.c Sat Nov 22 18:50:04 1997
@@ -39,6 +39,7 @@
*/
#include "npx.h"
+#include "opt_cpu.h" /* XXX */
#include "opt_sysvipc.h"
#include "opt_ddb.h"
#include "opt_bounce.h"
@@ -206,6 +207,13 @@
* Good {morning,afternoon,evening,night}.
*/
printf(version);
+#if defined(I586_CPU)
+ if (cpu == CPU_586) {
+ unsigned *pte = (unsigned *)vtopte(idt);
+ *pte &= ~PG_V;
+ printf("Pentium -- enable workaround for f00f problem!\n");
+ }
+#endif defined(I586_CPU)
earlysetcpuclass();
startrtclock();
identifycpu();
--- exception.s-ORIG Mon Aug 12 02:41:23 1996
+++ exception.s Sat Nov 22 18:44:22 1997
@@ -33,6 +33,7 @@
* $Id: exception.s,v 1.19 1996/08/11 17:41:23 davidg Exp $
*/
+#include "opt_cpu.h" /* XXX */
#include "npx.h" /* NNPX */
#include "assym.s" /* system defines */
#include <sys/errno.h> /* error return codes */
@@ -42,6 +43,9 @@
#include <sys/syscall.h> /* syscall numbers */
#include <machine/asmacros.h> /* miscellaneous macros */
#include <sys/cdefs.h> /* CPP macros */
+#if defined(I586_CPU)
+#include <machine/cputypes.h>
+#endif /* defined(I586) */
#define KDSEL 0x10 /* kernel data selector */
#define SEL_RPL_MASK 0x0003
@@ -112,6 +116,39 @@
IDTVEC(prot)
TRAP(T_PROTFLT)
IDTVEC(page)
+#if defined(I586_CPU)
+#define IDTVECnm(name) __CONCAT(_X,name)
+ /* data segment is not KERNEL ! */
+ pushl %eax
+ cmpl $CPU_586,%cs:_cpu
+ jne 1f
+ movl %cr2,%eax
+ subl $_idt,%eax
+ shrl $3,%eax
+ cmpl $6,%eax
+ ja 1f
+ /*
+ * page fault via accessing idt[0] to idt[6]
+ * dispatch to them
+ */
+ movl %cs:trp_vec(,%eax,4),%eax
+ movl %eax,4(%esp) /* holding error code */
+ popl %eax
+ addl $4,%esp /* adjust stack to discard error code */
+ jmp *-4(%esp)
+trp_vec:
+ /* order must be the same as in machdep.c */
+ .long IDTVECnm(div)
+ .long IDTVECnm(dbg)
+ .long IDTVECnm(nmi)
+ .long IDTVECnm(bpt)
+ .long IDTVECnm(ofl)
+ .long IDTVECnm(bnd)
+ .long IDTVECnm(ill)
+#undef IDTVECnm
+1:
+ popl %eax
+#endif /* defined(I586_CPU) */
TRAP(T_PAGEFLT)
IDTVEC(mchk)
pushl $0; TRAP(T_MCHK)
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