hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events

[mirror_ubuntu-zesty-kernel.git] / arch / x86 / kernel / process_32.c

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 209e74801763b7e747c37c687a8597305ef1b462..d5bd3132ee706d764510eec5058cf3e214cb2cc2 100644 (file)
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -59,7 +59,6 @@
 #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");
 
@@ -264,9 +263,8 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
        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;
+
+       memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 
        if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
                p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
@@ -287,13 +285,10 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
                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;
@@ -437,23 +432,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
                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;
 }