• Mohit Gambhir's avatar
    x86/xen: Fix APIC id mismatch warning on Intel · c07479f4
    Mohit Gambhir authored
    commit cc272163 upstream.
    
    This patch fixes the following warning message seen when booting the
    kernel as Dom0 with Xen on Intel machines.
    
    [0.003000] [Firmware Bug]: CPU1: APIC id mismatch. Firmware: 0 APIC: 1]
    
    The code generating the warning in validate_apic_and_package_id() matches
    cpu_data(cpu).apicid (initialized in init_intel()->
    detect_extended_topology() using cpuid) against the apicid returned from
    xen_apic_read(). Now, xen_apic_read() makes a hypercall to retrieve apicid
    for the boot  cpu but returns 0 otherwise. Hence the warning gets thrown
    for all but the boot cpu.
    
    The idea behind xen_apic_read() returning 0 for apicid is that the
    guests (even Dom0) should not need to know what physical processor their
    vcpus are running on. This is because we currently  do not have topology
    information in Xen and also because xen allows more vcpus than physical
    processors. However, boot cpu's apicid is required for loading
    xen-acpi-processor driver on AMD machines. Look at following patch for
    details:
    
    commit 558daa28 ("xen/apic: Return the APIC ID (and version) for CPU
    0.")
    
    So to get rid of the warning, this patch modifies
    xen_cpu_present_to_apicid() to return cpu_data(cpu).apicid instead of
    calling xen_apic_read().
    
    The warning is not seen on AMD machines because init_amd() populates
    cpu_data(cpu).apicid by calling hard_smp_processor_id()->xen_apic_read()
    as opposed to using apicid from cpuid as is done on Intel machines.
    Signed-off-by: default avatarMohit Gambhir <mohit.gambhir@oracle.com>
    Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
    Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Ben Hutchings <ben@decadent.org.uk>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    c07479f4
apic.c 5.11 KB