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Subject[tip: x86/urgent] x86/bus_lock: Don't assume the init value of DEBUGCTLMSR.BUS_LOCK_DETECT to be zero
The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: ffa6482e461ff550325356ae705b79e256702ea9
Gitweb: https://git.kernel.org/tip/ffa6482e461ff550325356ae705b79e256702ea9
Author: Chenyi Qiang <chenyi.qiang@intel.com>
AuthorDate: Tue, 02 Aug 2022 11:32:06 +08:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 02 Aug 2022 13:42:00 +02:00

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: ebb1064e7c2e ("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
---
arch/x86/kernel/cpu/intel.c | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 663f6e6..2d7ea54 100644
--- 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);
}

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