Re: [PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline

[Tom Lendacky]

On 2/28/2018 4:28 AM, Borislav Petkov wrote:
> From: Ashok Raj <ashok....@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....@intel.com>
> Cc: x86-ml <x...@kernel.org>
> Link: 
> http://lkml.kernel.org/r/1519352533-15992-4-git-send-email-ashok....@intel.com
> [ Massage it. ]
> Signed-off-by: Borislav Petkov <b...@suse.de>
> ---
>  arch/x86/kernel/cpu/microcode/core.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 

Reviewed-by: Tom Lendacky <thomas.lenda...@amd.com>

> 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)
>