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    Subject[PATCH 4.17 97/97] x86/microcode: Allow late microcode loading with SMT disabled
    Date
    4.17-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Josh Poimboeuf <jpoimboe@redhat.com>

    commit 07d981ad4cf1e78361c6db1c28ee5ba105f96cc1 upstream

    The kernel unnecessarily prevents late microcode loading when SMT is
    disabled. It should be safe to allow it if all the primary threads are
    online.

    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Acked-by: Borislav Petkov <bp@suse.de>
    Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kernel/cpu/microcode/core.c | 16 ++++++++++++----
    1 file changed, 12 insertions(+), 4 deletions(-)

    --- a/arch/x86/kernel/cpu/microcode/core.c
    +++ b/arch/x86/kernel/cpu/microcode/core.c
    @@ -509,12 +509,20 @@ static struct platform_device *microcode

    static int check_online_cpus(void)
    {
    - if (num_online_cpus() == num_present_cpus())
    - return 0;
    + unsigned int cpu;

    - pr_err("Not all CPUs online, aborting microcode update.\n");
    + /*
    + * Make sure all CPUs are online. It's fine for SMT to be disabled if
    + * all the primary threads are still online.
    + */
    + for_each_present_cpu(cpu) {
    + if (topology_is_primary_thread(cpu) && !cpu_online(cpu)) {
    + pr_err("Not all CPUs online, aborting microcode update.\n");
    + return -EINVAL;
    + }
    + }

    - return -EINVAL;
    + return 0;
    }

    static atomic_t late_cpus_in;

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