Re: [PATCH -v2 1/2] x86, microcode: Sanitize per-cpu microcode reloading interface

[Borislav Petkov <bp@amd64.org>]

On Tue, Jun 26, 2012 at 11:46:18PM +0200, Peter Zijlstra wrote:
> --- a/arch/x86/kernel/microcode_core.c
> +++ b/arch/x86/kernel/microcode_core.c
> @@ -87,6 +87,7 @@
>  #include <asm/microcode.h>
>  #include <asm/processor.h>
>  #include <asm/cpu_device_id.h>
> +#include <asm/perf_event.h>
>  
>  MODULE_DESCRIPTION("Microcode Update Driver");
>  MODULE_AUTHOR("Tigran Aivazian <tigran@aivazian.fsnet.co.uk>");
> @@ -277,7 +278,6 @@ static int reload_for_cpu(int cpu)
>  	struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
>  	int err = 0;
>  
> -	mutex_lock(&microcode_mutex);
>  	if (uci->valid) {
>  		enum ucode_state ustate;
>  
> @@ -288,7 +288,6 @@ static int reload_for_cpu(int cpu)
>  			if (ustate == UCODE_ERROR)
>  				err = -EINVAL;
>  	}
> -	mutex_unlock(&microcode_mutex);
>  
>  	return err;
>  }
> @@ -309,6 +308,7 @@ static ssize_t reload_store(struct devic
>  		return size;
>  
>  	get_online_cpus();
> +	mutex_lock(&microcode_mutex);
>  	for_each_online_cpu(cpu) {
>  		tmp_ret = reload_for_cpu(cpu);
>  		if (tmp_ret != 0)
> @@ -318,6 +318,9 @@ static ssize_t reload_store(struct devic
>  		if (!ret)
>  			ret = tmp_ret;
>  	}
> +	if (!ret)
> +		perf_check_microcode();
> +	mutex_unlock(&microcode_mutex);

In thinking about this a bit more, perf callback is only run from the
reload_store interface but we don't run it on module init time.

In the situation where perf is enabled, _then_ the microcode driver
is loaded as a module later, we don't get to run the callback
perf_check_microcode() even when we're loading the module and there's
new ucode on the system.

Maybe this needs to be called additionally in microcode_init() after
subsys_interface_register call which does microcode_init_cpu down its
path and should have updated the microcode when it is done registering
all the cpus...

Hmm.

-- 
Regards/Gruss,
Boris.

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