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    Subject[PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline
    Date
    From: Ashok Raj <ashok.raj@intel.com>

    Avoid loading microcode if any of the CPUs are offline, and issue a
    warning. Having different microcode revisions on the system at any time
    is outright dangerous.

    Signed-off-by: Ashok Raj <ashok.raj@intel.com>
    Cc: x86-ml <x86@kernel.org>
    Link: http://lkml.kernel.org/r/1519352533-15992-4-git-send-email-ashok.raj@intel.com
    [ Massage it. ]
    Signed-off-by: Borislav Petkov <bp@suse.de>
    ---
    arch/x86/kernel/cpu/microcode/core.c | 18 ++++++++++++++++++
    1 file changed, 18 insertions(+)

    diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
    index 63370651e376..fa32cb3dcca5 100644
    --- a/arch/x86/kernel/cpu/microcode/core.c
    +++ b/arch/x86/kernel/cpu/microcode/core.c
    @@ -486,6 +486,16 @@ static void __exit microcode_dev_exit(void)
    /* fake device for request_firmware */
    static struct platform_device *microcode_pdev;

    +static int check_online_cpus(void)
    +{
    + if (num_online_cpus() == num_present_cpus())
    + return 0;
    +
    + pr_err("Not all CPUs online, aborting microcode update.\n");
    +
    + return -EINVAL;
    +}
    +
    static enum ucode_state reload_for_cpu(int cpu)
    {
    struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
    @@ -519,7 +529,13 @@ static ssize_t reload_store(struct device *dev,
    return size;

    get_online_cpus();
    +
    + ret = check_online_cpus();
    + if (ret)
    + goto put;
    +
    mutex_lock(&microcode_mutex);
    +
    for_each_online_cpu(cpu) {
    tmp_ret = reload_for_cpu(cpu);
    if (tmp_ret > UCODE_NFOUND) {
    @@ -538,6 +554,8 @@ static ssize_t reload_store(struct device *dev,
    microcode_check();

    mutex_unlock(&microcode_mutex);
    +
    +put:
    put_online_cpus();

    if (!ret)
    --
    2.13.0
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