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    SubjectRe: [tip:x86/urgent] x86, apic: Don't use logical-flat mode when CPU hotplug may exceed 8 CPUs
    On 02/09/2010 10:00 AM, tip-bot for Suresh Siddha wrote:
    > Commit-ID: 418f727639cfc8f03068aae09f473c493c759b9b
    > Gitweb: http://git.kernel.org/tip/418f727639cfc8f03068aae09f473c493c759b9b
    > Author: Suresh Siddha <suresh.b.siddha@intel.com>
    > AuthorDate: Tue, 9 Feb 2010 09:18:35 -0800
    > Committer: H. Peter Anvin <hpa@zytor.com>
    > CommitDate: Tue, 9 Feb 2010 09:29:17 -0800
    >
    > x86, apic: Don't use logical-flat mode when CPU hotplug may exceed 8 CPUs
    >
    > We need to fall back from logical-flat APIC mode to physical-flat mode
    > when we have more than 8 CPUs. However, in the presence of CPU
    > hotplug, we have to consider the number of possible CPUs rather than
    > the number of current CPUs; otherwise we may cross the 8-CPU boundary
    > when CPUs are added later.
    >
    > Reported-by: Shaohui Zheng <shaohui.zheng@intel.com>
    > Acked-by: Shaohui Zheng <shaohui.zheng@intel.com>
    > Cc: Yinghai Lu <yinghai@kernel.org>
    > LKML-Reference: <20100118201256.672679042@sbs-t61.sc.intel.com>
    > Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    > Cc: <stable@kernel.org>
    > ---
    > arch/x86/kernel/apic/apic.c | 2 +-
    > arch/x86/kernel/apic/probe_64.c | 2 +-
    > 2 files changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
    > index 3987e44..fc1d579 100644
    > --- a/arch/x86/kernel/apic/apic.c
    > +++ b/arch/x86/kernel/apic/apic.c
    > @@ -1892,7 +1892,7 @@ void __cpuinit generic_processor_info(int apicid, int version)
    > max_physical_apicid = apicid;
    >
    > #ifdef CONFIG_X86_32
    > - if (num_processors > 8) {
    > + if (num_possible_cpus() > 8) {

    for 32bit you can not use this function yet.
    that only can be used after prefill_possible_map()

    > switch (boot_cpu_data.x86_vendor) {
    > case X86_VENDOR_INTEL:
    > if (!APIC_XAPIC(version)) {
    > diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
    > index 450fe20..83e9be4 100644
    > --- a/arch/x86/kernel/apic/probe_64.c
    > +++ b/arch/x86/kernel/apic/probe_64.c
    > @@ -67,7 +67,7 @@ void __init default_setup_apic_routing(void)
    > }
    > #endif
    >
    > - if (apic == &apic_flat && num_processors > 8)
    > + if (apic == &apic_flat && num_possible_cpus() > 8)
    > apic = &apic_physflat;
    >
    > printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);

    please check
    http://patchwork.kernel.org/patch/74536/
    http://patchwork.kernel.org/patch/74533/
    http://patchwork.kernel.org/patch/74525/
    http://patchwork.kernel.org/patch/74524/

    YH


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