Commit 558682b5 authored by Bandan Das's avatar Bandan Das Committed by Thomas Gleixner
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x86/apic: Include the LDR when clearing out APIC registers

Although APIC initialization will typically clear out the LDR before
setting it, the APIC cleanup code should reset the LDR.

This was discovered with a 32-bit KVM guest jumping into a kdump
kernel. The stale bits in the LDR triggered a bug in the KVM APIC
implementation which caused the destination mapping for VCPUs to be

Note that this isn't intended to paper over the KVM APIC bug. The kernel
has to clear the LDR when resetting the APIC registers except when X2APIC
is enabled.

This lacks a Fixes tag because missing to clear LDR goes way back into pre
git history.

[ tglx: Made x2apic_enabled a function call as required ]

Signed-off-by: default avatarBandan Das <>
Signed-off-by: default avatarThomas Gleixner <>
parent bae3a8d3
......@@ -1179,6 +1179,10 @@ void clear_local_APIC(void)
apic_write(APIC_LVT0, v | APIC_LVT_MASKED);
v = apic_read(APIC_LVT1);
apic_write(APIC_LVT1, v | APIC_LVT_MASKED);
if (!x2apic_enabled()) {
v = apic_read(APIC_LDR) & ~APIC_LDR_MASK;
apic_write(APIC_LDR, v);
if (maxlvt >= 4) {
v = apic_read(APIC_LVTPC);
apic_write(APIC_LVTPC, v | APIC_LVT_MASKED);
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