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Subject[tip:x86/apic] x86/apic: Soft disable APIC before initializing it
Commit-ID:  2640da4cccf5cc613bf26f0998b9e340f4b5f69c
Gitweb: https://git.kernel.org/tip/2640da4cccf5cc613bf26f0998b9e340f4b5f69c
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Mon, 22 Jul 2019 20:47:08 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 25 Jul 2019 16:11:56 +0200

x86/apic: Soft disable APIC before initializing it

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@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190722105219.068290579@linutronix.de

---
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 fa0846d4e000..621992de49ee 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1522,6 +1522,14 @@ 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) {
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