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    SubjectRe: 2.6.35 hangs on early boot in KVM
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    Gleb Natapov <gleb@redhat.com> writes:

    > On Wed, Aug 04, 2010 at 10:16:08AM +0100, Tvrtko Ursulin wrote:
    >>
    >> Not the tip but 2.6.35 with earlyprintk=ttyS0,115200:
    >>
    >> [ 0.000000] Processor #0 (Bootup-CPU)
    >> [ 0.000000] I/O APIC #1 Version 17 at 0xFEC00000.
    >> [ 0.000000] BUG: unable to handle kernel paging request at ffffb030
    >> [ 0.000000] IP: [<c011d136>] native_apic_mem_read+0x16/0x20
    >> [ 0.000000] *pde = 00832067 *pte = 00000000
    > Accessing APIC version register before APIC is mapped.

    Yep. I see it now. We have some of the silliest code. We only
    go down this path for certain revs of Intel cpus, and I double checked
    this change on an AMD cpu which explains why I missed hitting this
    case.

    The call path that is new in they bisected commit is:
    MP_ioapic_info()
    mp_register_ioapic()
    io_apic_unique_id()
    io_apic_get_unique_id()
    get_physical_broadcast()
    modern_apic()
    lapic_get_version()
    apic_read(APIC_LVR)


    Tvrtko can you test this patch and verify it fixes the kvm booting
    issue?

    This patch just maps the lapic early in the mmparse.c just like we
    do in acpi/boot.c when parsing the acpi tables.

    Eric


    ---

    diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
    index a96489e..c07e513 100644
    --- a/arch/x86/kernel/apic/apic.c
    +++ b/arch/x86/kernel/apic/apic.c
    @@ -1606,7 +1606,7 @@ void __init init_apic_mappings(void)
    * acpi lapic path already maps that address in
    * acpi_register_lapic_address()
    */
    - if (!acpi_lapic)
    + if (!acpi_lapic && !smp_found_config)
    set_fixmap_nocache(FIX_APIC_BASE, apic_phys);

    apic_printk(APIC_VERBOSE, "mapped APIC to %08lx (%08lx)\n",
    diff --git a/arch/x86/kernel/mpparse.c b/arch/x86/kernel/mpparse.c
    index d86dbf7..d7b6f7f 100644
    --- a/arch/x86/kernel/mpparse.c
    +++ b/arch/x86/kernel/mpparse.c
    @@ -274,6 +274,18 @@ static void __init smp_dump_mptable(struct mpc_table *mpc, unsigned char *mpt)

    void __init default_smp_read_mpc_oem(struct mpc_table *mpc) { }

    +static void __init smp_register_lapic_address(unsigned long address)
    +{
    + mp_lapic_addr = address;
    +
    + set_fixmap_nocache(FIX_APIC_BASE, address);
    + if (boot_cpu_physical_apicid == -1U) {
    + boot_cpu_physical_apicid = read_apic_id();
    + apic_version[boot_cpu_physical_apicid] =
    + GET_APIC_VERSION(apic_read(APIC_LVR));
    + }
    +}
    +
    static int __init smp_read_mpc(struct mpc_table *mpc, unsigned early)
    {
    char str[16];
    @@ -295,6 +307,10 @@ static int __init smp_read_mpc(struct mpc_table *mpc, unsigned early)
    if (early)
    return 1;

    + /* Initialize the lapic mapping */
    + if (!acpi_lapic)
    + smp_register_lapic_address(mpc->lapic);
    +
    if (mpc->oemptr)
    x86_init.mpparse.smp_read_mpc_oem(mpc);



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