linux-kernel - [PATCH AUTOSEL 5.2 028/185] x86/apic: Soft disable APIC before initializing it

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Message-Id: <20190922184924.32534-28-sashal@kernel.org>
Date:   Sun, 22 Sep 2019 14:46:46 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.2 028/185] x86/apic: Soft disable APIC before initializing it

From: Thomas Gleixner <tglx@...utronix.de>

[ Upstream commit 2640da4cccf5cc613bf26f0998b9e340f4b5f69c ]

If the APIC was already enabled on entry of setup_local_APIC() then
disabling it soft via the SPIV register makes a lot of sense.

That masks all LVT entries and brings it into a well defined state.

Otherwise previously enabled LVTs which are not touched in the setup
function stay unmasked and might surprise the just booting kernel.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20190722105219.068290579@linutronix.de
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kernel/apic/apic.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 67d1259e0f7c0..a18d6dd934e55 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1550,6 +1550,14 @@ static void setup_local_APIC(void)
 		return;
 	}
 
+	/*
+	 * If this comes from kexec/kcrash the APIC might be enabled in
+	 * SPIV. Soft disable it before doing further initialization.
+	 */
+	value = apic_read(APIC_SPIV);
+	value &= ~APIC_SPIV_APIC_ENABLED;
+	apic_write(APIC_SPIV, value);
+
 #ifdef CONFIG_X86_32
 	/* Pound the ESR really hard over the head with a big hammer - mbligh */
 	if (lapic_is_integrated() && apic->disable_esr) {
-- 
2.20.1