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

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

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 663f6e6dd288650b198ebf89c95f4257e862f715..2d7ea5480ec3394d7422b7c06df98d759ed8ad84 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1216,22 +1216,23 @@ static void bus_lock_init(void)
 {
        u64 val;
 
-       /*
-        * Warn and fatal are handled by #AC for split lock if #AC for
-        * split lock is supported.
-        */
-       if (!boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT) ||
-           (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
-           (sld_state == sld_warn || sld_state == sld_fatal)) ||
-           sld_state == sld_off)
+       if (!boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT))
                return;
 
-       /*
-        * Enable #DB for bus lock. All bus locks are handled in #DB except
-        * split locks are handled in #AC in the fatal case.
-        */
        rdmsrl(MSR_IA32_DEBUGCTLMSR, val);
-       val |= DEBUGCTLMSR_BUS_LOCK_DETECT;
+
+       if ((boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
+           (sld_state == sld_warn || sld_state == sld_fatal)) ||
+           sld_state == sld_off) {
+               /*
+                * Warn and fatal are handled by #AC for split lock if #AC for
+                * split lock is supported.
+                */
+               val &= ~DEBUGCTLMSR_BUS_LOCK_DETECT;
+       } else {
+               val |= DEBUGCTLMSR_BUS_LOCK_DETECT;
+       }
+
        wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
 }