x86/apic: Include the LDR when clearing out APIC registers

commit 558682b5291937a70748d36fd9ba757fb25b99ae upstream.

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
corrupted.

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: Bandan Das <bsd@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20190826101513.5080-3-bsd@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b316bd61a6aced7f865b069e481b59c12fbc802d..90be3a1506d3f0067559d0956e3f29d474c7c6bf 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1140,6 +1140,10 @@ 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);