hw-breakpoints: use the new wrapper routines to access debug registers in process/thread code
This patch enables the use of abstract debug registers in
process-handling routines, according to the new hardware breakpoint
Api.
[ Impact: adapt thread breakpoints handling code to the new breakpoint Api ]
Original-patch-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index b5e4bfe..297ffff 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -61,6 +61,8 @@
#include <asm/idle.h>
#include <asm/syscalls.h>
#include <asm/ds.h>
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
@@ -265,7 +267,13 @@
task_user_gs(p) = get_user_gs(regs);
+ p->thread.io_bitmap_ptr = NULL;
tsk = current;
+ err = -ENOMEM;
+ if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG)))
+ if (copy_thread_hw_breakpoint(tsk, p, clone_flags))
+ goto out;
+
if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
IO_BITMAP_BYTES, GFP_KERNEL);
@@ -285,10 +293,13 @@
err = do_set_thread_area(p, -1,
(struct user_desc __user *)childregs->si, 0);
+out:
if (err && p->thread.io_bitmap_ptr) {
kfree(p->thread.io_bitmap_ptr);
p->thread.io_bitmap_max = 0;
}
+ if (err)
+ flush_thread_hw_breakpoint(p);
clear_tsk_thread_flag(p, TIF_DS_AREA_MSR);
p->thread.ds_ctx = NULL;
@@ -427,6 +438,23 @@
lazy_load_gs(next->gs);
percpu_write(current_task, next_p);
+ /*
+ * There's a problem with moving the arch_install_thread_hw_breakpoint()
+ * call before current is updated. Suppose a kernel breakpoint is
+ * triggered in between the two, the hw-breakpoint handler will see that
+ * the 'current' task does not have TIF_DEBUG flag set and will think it
+ * is leftover from an old task (lazy switching) and will erase it. Then
+ * until the next context switch, no user-breakpoints will be installed.
+ *
+ * The real problem is that it's impossible to update both current and
+ * physical debug registers at the same instant, so there will always be
+ * a window in which they disagree and a breakpoint might get triggered.
+ * Since we use lazy switching, we are forced to assume that a
+ * disagreement means that current is correct and the exception is due
+ * to lazy debug register switching.
+ */
+ if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG)))
+ arch_install_thread_hw_breakpoint(next_p);
return prev_p;
}