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Subject[RFC PATCH v2 64/69] cpu/hotplug: Document that TDX also depends on booting CPUs once
Date
From: Kai Huang <kai.huang@linux.intel.com>

Add a comment to explain that TDX also depends on booting logical CPUs
at least once.

TDSYSINITLP must be run on all CPUs, even software disabled CPUs in the
-nosmt case. Fortunately, current SMT handling for #MC already supports
booting all CPUs once; the to-be-disabled sibling is booted once (and
later put into deep C-state to honor SMT=off) to allow the init code to
set CR4.MCE and avoid an unwanted shutdown on a broadcasted MCE.

Signed-off-by: Kai Huang <kai.huang@linux.intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
kernel/cpu.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index e538518556f4..58377a03e9d6 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -446,6 +446,10 @@ static inline bool cpu_smt_allowed(unsigned int cpu)
* that the init code can get a chance to set CR4.MCE on each
* CPU. Otherwise, a broadcasted MCE observing CR4.MCE=0b on any
* core will shutdown the machine.
+ *
+ * Intel TDX also requires running TDH_SYS_LP_INIT on all logical CPUs
+ * during boot, booting all CPUs once allows TDX to play nice with
+ * 'nosmt'.
*/
return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
}
--
2.25.1
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