Restriction on setting debug registers (HW breakpoint) at kernel space

[Probir Roy]

Hi,

I am patching the perf tool of linux to set HW breakpoints at kernel
space. I found that there is an interface for user-space
(modify_user_hw_breakpoint) but no interface for system wide
breakpoint modification. Older version of linux had this support by K.
Prasad. I was wondering why linux remove this support. Moreover, when
I patch the perf tool for kernel space breakpoint following steps from
"modify_user_hw_breakpoint", kernel panics but nothing is written on
log file. What could be the issue? Is it a race condition while
modifying the address or is it because kernel restricts it to set HW
breakpoint at some kernel address(if so, where is it written)?

Regards
-- 
Probir Roy