x86, 64-bit: Move K8 B step iret fixup to fault entry asm

Move the handling of truncated %rip from an iret fault to the fault
entry path.

This allows x86-64 to use the standard search_extable() function.
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <1255357103-5418-1-git-send-email-brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
(cherry picked from commit ae24ffe5)
[wt: only merged to fix patch context and ease merging of next patches]
Signed-off-by: Willy Tarreau <w@1wt.eu>

arch/x86/include/asm/uaccess.h

@@ -570,7 +570,6 @@ extern struct movsl_mask {
 #ifdef CONFIG_X86_32
 # include "uaccess_32.h"
 #else
-# define ARCH_HAS_SEARCH_EXTABLE
 # include "uaccess_64.h"
 #endif
 

arch/x86/kernel/entry_64.S

@@ -1491,12 +1491,17 @@ error_kernelspace:
 	leaq irq_return(%rip),%rcx
 	cmpq %rcx,RIP+8(%rsp)
 	je error_swapgs
-	movl %ecx,%ecx	/* zero extend */
-	cmpq %rcx,RIP+8(%rsp)
-	je error_swapgs
+	movl %ecx,%eax	/* zero extend */
+	cmpq %rax,RIP+8(%rsp)
+	je bstep_iret
 	cmpq $gs_change,RIP+8(%rsp)
 	je error_swapgs
 	jmp error_sti
+
+bstep_iret:
+	/* Fix truncated RIP */
+	movq %rcx,RIP+8(%rsp)
+	je error_swapgs
 END(error_entry)
 
 

arch/x86/mm/extable.c

@@ -35,34 +35,3 @@ int fixup_exception(struct pt_regs *regs)
 
 	return 0;
 }
-
-#ifdef CONFIG_X86_64
-/*
- * Need to defined our own search_extable on X86_64 to work around
- * a B stepping K8 bug.
- */
-const struct exception_table_entry *
-search_extable(const struct exception_table_entry *first,
-	       const struct exception_table_entry *last,
-	       unsigned long value)
-{
-	/* B stepping K8 bug */
-	if ((value >> 32) == 0)
-		value |= 0xffffffffUL << 32;
-
-	while (first <= last) {
-		const struct exception_table_entry *mid;
-		long diff;
-
-		mid = (last - first) / 2 + first;
-		diff = mid->insn - value;
-		if (diff == 0)
-			return mid;
-		else if (diff < 0)
-			first = mid+1;
-		else
-			last = mid-1;
-	}
-	return NULL;
-}
-#endif