x86/bus_lock: Don't assume the init value of DEBUGCTLMSR.BUS_LOCK_DETECT to be zero

x86/bus_lock: Don't assume the init value of DEBUGCTLMSR.BUS_LOCK_DETECT to be zero

[ Upstream commit ea37b5e7ec50de581ba2c6df2becc80c6d697a26 ]

It's possible that this kernel has been kexec'd from a kernel that
enabled bus lock detection, or (hypothetically) BIOS/firmware has set
DEBUGCTLMSR_BUS_LOCK_DETECT.

Disable bus lock detection explicitly if not wanted.

Fixes: b817401736f3 ("x86/traps: Handle #DB for bus lock")
Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20220802033206.21333-1-chenyi.qiang@intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>