x86-32: Rework cache flush denied handler

The cache flush denied error is an erratum on some AMD 486 clones.  If an invd
instruction is executed in userspace, the processor calls exception 19 (13 hex)
instead of #GP (13 decimal).  On cpus where XMM is not supported, redirect
exception 19 to do_general_protection().  Also, remove die_if_kernel(), since
this was the last user.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1269176446-2489-2-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/Kconfig.cpu

@@ -338,6 +338,10 @@ config X86_F00F_BUG
 	def_bool y
 	depends on M586MMX || M586TSC || M586 || M486 || M386
 
+config X86_INVD_BUG
+	def_bool y
+	depends on M486 || M386
+
 config X86_WP_WORKS_OK
 	def_bool y
 	depends on !M386

arch/x86/kernel/entry_32.S

@@ -53,6 +53,7 @@
 #include <asm/processor-flags.h>
 #include <asm/ftrace.h>
 #include <asm/irq_vectors.h>
+#include <asm/cpufeature.h>
 
 /* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
 #include <linux/elf-em.h>
@@ -905,7 +906,25 @@ ENTRY(simd_coprocessor_error)
 	RING0_INT_FRAME
 	pushl $0
 	CFI_ADJUST_CFA_OFFSET 4
+#ifdef CONFIG_X86_INVD_BUG
+	/* AMD 486 bug: invd from userspace calls exception 19 instead of #GP */
+661:	pushl $do_general_protection
+662:
+.section .altinstructions,"a"
+	.balign 4
+	.long 661b
+	.long 663f
+	.byte X86_FEATURE_XMM
+	.byte 662b-661b
+	.byte 664f-663f
+.previous
+.section .altinstr_replacement,"ax"
+663:	pushl $do_simd_coprocessor_error
+664:
+.previous
+#else
 	pushl $do_simd_coprocessor_error
+#endif
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp error_code
 	CFI_ENDPROC

arch/x86/kernel/traps.c

@@ -108,15 +108,6 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 	dec_preempt_count();
 }
 
-#ifdef CONFIG_X86_32
-static inline void
-die_if_kernel(const char *str, struct pt_regs *regs, long err)
-{
-	if (!user_mode_vm(regs))
-		die(str, regs, err);
-}
-#endif
-
 static void __kprobes
 do_trap(int trapnr, int signr, char *str, struct pt_regs *regs,
 	long error_code, siginfo_t *info)
@@ -729,30 +720,14 @@ do_simd_coprocessor_error(struct pt_regs *regs, long error_code)
 	conditional_sti(regs);
 
 #ifdef CONFIG_X86_32
-	if (cpu_has_xmm) {
-		/* Handle SIMD FPU exceptions on PIII+ processors. */
-		ignore_fpu_irq = 1;
-		simd_math_error((void __user *)regs->ip);
-		return;
-	}
-	/*
-	 * Handle strange cache flush from user space exception
-	 * in all other cases.  This is undocumented behaviour.
-	 */
-	if (regs->flags & X86_VM_MASK) {
-		handle_vm86_fault((struct kernel_vm86_regs *)regs, error_code);
-		return;
-	}
-	current->thread.trap_no = 19;
-	current->thread.error_code = error_code;
-	die_if_kernel("cache flush denied", regs, error_code);
-	force_sig(SIGSEGV, current);
+	ignore_fpu_irq = 1;
 #else
 	if (!user_mode(regs) &&
 			kernel_math_error(regs, "kernel simd math error", 19))
 		return;
-	simd_math_error((void __user *)regs->ip);
 #endif
+
+	simd_math_error((void __user *)regs->ip);
 }
 
 dotraplinkage void