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. Signed-off-by: Bandan Das <[email protected]> [Linux commit 558682b5291937a70748d36fd9ba757fb25b99ae] Signed-off-by: Jan Beulich <[email protected]> --- a/xen/arch/x86/apic.c +++ b/xen/arch/x86/apic.c @@ -212,6 +212,10 @@ void clear_local_APIC(void) apic_write(APIC_LVTTHMR, APIC_LVT_MASKED); if (maxlvt >= 6) apic_write(APIC_CMCI, APIC_LVT_MASKED); + if (!x2apic_enabled) { + v = apic_read(APIC_LDR) & ~APIC_LDR_MASK; + apic_write(APIC_LDR, v); + } if (maxlvt > 3) /* Due to Pentium errata 3AP and 11AP. */ apic_write(APIC_ESR, 0); _______________________________________________ Xen-devel mailing list [email protected] https://lists.xenproject.org/mailman/listinfo/xen-devel
