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

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index fa0846d..621992d 100644 (file)
--- 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) {