commit 5fd75ebb1a58c1a3c9e3d9fdf75ce7286b79bb74
author Petr Tesarik <kernel@tesarici.cz> Sat Sep 03 15:56:28 2005 -0700
committer Linus Torvalds <torvalds@evo.osdl.org> Mon Sep 05 00:06:09 2005 -0700
tree 9597e94f20ba1fa317cc05c450e43c8fe80f39ea
parent 7ae65fd334232468a9d6b523a4fc141cd6ec5ea4

[PATCH] vm86: Honor TF bit when emulating an instruction

If the virtual 86 machine reaches an instruction which raises a General
Protection Fault (such as CLI or STI), the instruction is emulated (in
handle_vm86_fault).  However, the emulation ignored the TF bit, so the
hardware debug interrupt was not invoked after such an emulated instruction
(and the DOS debugger missed it).

This patch fixes the problem by emulating the hardware debug interrupt as
the last action before control is returned to the VM86 program.

Signed-off-by: Petr Tesarik <kernel@tesarici.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/vm86.c

diff --git a/arch/i386/kernel/vm86.c b/arch/i386/kernel/vm86.c
index ec0f68c..2daa06f 100644
--- a/arch/i386/kernel/vm86.c
+++ b/arch/i386/kernel/vm86.c
@@ -542,7 +542,7 @@
 	unsigned char opcode;
 	unsigned char __user *csp;
 	unsigned char __user *ssp;
-	unsigned short ip, sp;
+	unsigned short ip, sp, orig_flags;
 	int data32, pref_done;
 
 #define CHECK_IF_IN_TRAP \
@@ -551,8 +551,12 @@
 #define VM86_FAULT_RETURN do { \
 	if (VMPI.force_return_for_pic  && (VEFLAGS & (IF_MASK | VIF_MASK))) \
 		return_to_32bit(regs, VM86_PICRETURN); \
+	if (orig_flags & TF_MASK) \
+		handle_vm86_trap(regs, 0, 1); \
 	return; } while (0)
 
+	orig_flags = *(unsigned short *)&regs->eflags;
+
 	csp = (unsigned char __user *) (regs->cs << 4);
 	ssp = (unsigned char __user *) (regs->ss << 4);
 	sp = SP(regs);