[RFC Patch 0/2][Bugfix][x86][hw-breakpoint] Bugfixes forhw_breakpoint_handler

[K.Prasad]

Hi All,
	Please find a patchset of two patches that

Patch 1/2: Clears the arch-reserved bits from debug status register. This
helps easy bitwise operations - such as the check for non-trap bits in
hw_breakpoint_handler. A check for the same using
"if (dr6 & (~DR_TRAP_BITS))" throws incorrect results due to the 
presence of preset reserved bits.

This patch is copied to maintainers of code (such as kmemcheck, kprobe,
ptrace, etc) who make use of local dr6 value in do_debug() that verify
and handle exceptions.

Patch 2/2: Return NOTIFY_DONE from hw_breakpoint_handler() for user-space
breakpoints only (and not for kernel-space) since this could lead to
further processing in do_debug() with undesirable consequences.

Let me know if there are any concerns about the patch.

Thanks,
K.Prasad

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