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

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Date:   Fri, 13 Oct 2017 10:07:48 -0400
From:   Probir Roy <proy.cse@...il.com>
To:     linux-kernel@...r.kernel.org, prasad@...ux.vnet.ibm.com,
        paulus@....ibm.com, tglx@...utronix.de
Subject: Restriction on setting debug registers (HW breakpoint) at kernel space

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