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From: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
To: <tglx@linutronix.de>, <mingo@redhat.com>, <bp@alien8.de>,
	<dave.hansen@linux.intel.com>, <x86@kernel.org>, <hpa@zytor.com>,
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	<alexandre.belloni@bootlin.com>, <mario.limonciello@amd.com>,
	<TonyWWang-oc@zhaoxin.com>, <yaolu@kylinos.cn>, <bhelgaas@google.com>,
	<justinstitt@google.com>, <linux-kernel@vger.kernel.org>,
	<linux-hardening@vger.kernel.org>
CC: <CobeChen@zhaoxin.com>, <TimGuo@zhaoxin.com>, <LeoLiu-oc@zhaoxin.com>
Subject: [PATCH] x86/hpet: Read HPET directly if panic in progress
Date: Tue, 28 May 2024 14:38:36 +0800
Message-ID: <20240528063836.5248-1-TonyWWang-oc@zhaoxin.com>
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When the clocksource of the system is HPET，a CPU executing read_hpet
might be interrupted by exceptions to executing the panic，this may
lead to read_hpet dead loops:

CPU x				    CPU x
----                                ----
read_hpet()
  arch_spin_trylock(&hpet.lock)
  [CPU x got the hpet.lock]         #MCE happened
				    do_machine_check()
				      mce_panic()
				        panic()
					  kmsg_dump()
					    pstore_dump()
					      pstore_record_init()
						ktime_get_real_fast_ns()
						  read_hpet()
						  [dead loops]

To avoid this dead loops, read HPET directly if panic in progress.

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
---
 arch/x86/kernel/hpet.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index c96ae8fee95e..ecadd0698d6a 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -804,6 +804,12 @@ static u64 read_hpet(struct clocksource *cs)
 	if (in_nmi())
 		return (u64)hpet_readl(HPET_COUNTER);
 
+	/*
+	 * Read HPET directly if panic in progress.
+	 */
+	if (unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID))
+		return (u64)hpet_readl(HPET_COUNTER);
+
 	/*
 	 * Read the current state of the lock and HPET value atomically.
 	 */
-- 
2.25.1