Re: [PATCH 3/3] x86/microcode: Quiesce all threads before a microcode update.

[Raj, Ashok]

On Wed, Feb 21, 2018 at 08:06:11PM +0100, Borislav Petkov wrote:
> >  arch/x86/kernel/cpu/microcode/core.c  | 113 +++++++++++++++++++++++++++++-----
> 
> This is generic so Tom needs to ack whatever we end up doing for the AMD
> side.

Yes, i did ping Tom to check if this is ok with them.

> 
> >  arch/x86/kernel/cpu/microcode/intel.c |   1 +
> >  2 files changed, 98 insertions(+), 16 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> > index aa1b9a4..af0aeb2 100644
> > --- a/arch/x86/kernel/cpu/microcode/core.c
> > +++ b/arch/x86/kernel/cpu/microcode/core.c
> > @@ -31,6 +31,9 @@
> >  #include <linux/cpu.h>
> >  #include <linux/fs.h>
> >  #include <linux/mm.h>
> > +#include <linux/nmi.h>
> > +#include <linux/stop_machine.h>
> > +#include <linux/delay.h>
> >  
> >  #include <asm/microcode_intel.h>
> >  #include <asm/cpu_device_id.h>
> > @@ -489,19 +492,82 @@ static void __exit microcode_dev_exit(void)
> >  /* fake device for request_firmware */
> >  static struct platform_device	*microcode_pdev;
> >  
> > -static enum ucode_state reload_for_cpu(int cpu)
> > +static struct ucode_update_param {
> > +	spinlock_t ucode_lock;
> > +	atomic_t   count;
> > +	atomic_t   errors;
> > +	atomic_t   enter;
> > +	int	   timeout;
> > +} uc_data;
> > +
> > +static void do_ucode_update(int cpu, struct ucode_update_param *ucd)
> >  {
> > -	struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
> > -	enum ucode_state ustate;
> > +	enum ucode_state retval = 0;
> >  
> > -	if (!uci->valid)
> > -		return UCODE_OK;
> > +	spin_lock(&ucd->ucode_lock);
> > +	retval = microcode_ops->apply_microcode(cpu);
> > +	spin_unlock(&ucd->ucode_lock);
> 
> What's the spinlock protecting against?

This is ensuring no 2 cpus do ucode update at the same time.

Since all cpus wait for all the online cpus to arrive in stop_machine handler.
Once we let go, every cpu tries to update. This just serializes against that.

> 
> We hold the hotplug lock and the microcode mutex. And yet interrupts are
> still enabled. So what's up?

hotplug lock/microcode mutex are at global level, these are 
protecting individual cpus in stop machine trying to update microcode.

these are called while in stop_machine() so i think interrupts are disabled IRC.

> 
> 
> > +	if (retval > UCODE_NFOUND) {
> > +		atomic_inc(&ucd->errors);
> 
> You don't need ->errors. Simply propagate retval from do_ucode_update().
> Or compare ucd->count to the number of CPUs. Or something like that.

That's what we are doing here, but simply returning number of cpus
that encountered failure instead of a per-cpu retval
like before.

I use ucd->count to use as an exit rendezvous.. to make sure we leave only
after all cpus have done updating ucode.

> > +		pr_warn("microcode update to cpu %d failed\n", cpu);
> > +	}
> > +	atomic_inc(&ucd->count);
> > +}
> > +
> > +/*
> > + * Wait for upto 1sec for all cpus
> > + * to show up in the rendezvous function
> > + */
> > +#define MAX_UCODE_RENDEZVOUS	1000000000 /* nanosec */
> 
> 				1 * NSEC_PER_SEC
> 
> > +#define SPINUNIT		100	   /* 100ns */
> > +
> > +/*
> > + * Each cpu waits for 1sec max.
> > + */
> > +static int ucode_wait_timedout(int *time_out, void *data)
> > +{
> > +	struct ucode_update_param *ucd = data;
> > +	if (*time_out < SPINUNIT) {
> > +		pr_err("Not all cpus entered ucode update handler %d cpus missing\n",
> > +			(num_online_cpus() - atomic_read(&ucd->enter)));
> > +		return 1;
> > +	}
> > +	*time_out -= SPINUNIT;
> > +	touch_nmi_watchdog();
> > +	return 0;
> > +}
> > +
> > +/*
> > + * All cpus enter here before a ucode load upto 1 sec.
> > + * If not all cpus showed up, we abort the ucode update
> > + * and return. ucode update is serialized with the spinlock
> 
> ... and yet you don't check stop_machine()'s retval and issue an error
> message that it failed.
> 

Will add that 

> > + */
> > +static int ucode_load_rendezvous(void *data)
> 
> The correct prefix is "microcode_"
> 
> > +{
> > +	int cpu = smp_processor_id();
> > +	struct ucode_update_param *ucd = data;
> > +	int timeout = MAX_UCODE_RENDEZVOUS;
> > +	int total_cpus = num_online_cpus();
> >  
> > -	ustate = microcode_ops->request_microcode_fw(cpu, &microcode_pdev->dev, true);
> > -	if (ustate != UCODE_OK)
> > -		return ustate;
> > +	/*
> > +	 * Wait for all cpu's to arrive
> > +	 */
> > +	atomic_dec(&ucd->enter);
> > +	while(atomic_read(&ucd->enter)) {
> > +		if (ucode_wait_timedout(&timeout, ucd))
> > +			return 1;
> > +		ndelay(SPINUNIT);
> > +	}
> > +
> > +	do_ucode_update(cpu, ucd);
> >  
> > -	return apply_microcode_on_target(cpu);
> > +	/*
> > +	 * Wait for all cpu's to complete
> > +	 * ucode update
> > +	 */
> > +	while (atomic_read(&ucd->count) != total_cpus)
> > +		cpu_relax();
> > +	return 0;
> >  }
> >  
> >  static ssize_t reload_store(struct device *dev,
> > @@ -509,7 +575,6 @@ static ssize_t reload_store(struct device *dev,
> >  			    const char *buf, size_t size)
> >  {
> >  	enum ucode_state tmp_ret = UCODE_OK;
> > -	bool do_callback = false;
> >  	unsigned long val;
> >  	ssize_t ret = 0;
> >  	int cpu;
> > @@ -523,21 +588,37 @@ static ssize_t reload_store(struct device *dev,
> >  
> >  	get_online_cpus();
> >  	mutex_lock(&microcode_mutex);
> > +	/*
> > +	 * First load the microcode file for all cpu's
> > +	 */
> 
> It is always "CPU" or "CPUs". Fix all misspelled places.
> 
> >  	for_each_online_cpu(cpu) {
> 
> You need to fail loading and not even try when not all cores are online.
> And issue an error message.
> 

When we online any of the offline cpu's we do a microcode load again right? 

I did check with offlining 2 threads of the same core offline, then reload with a 
new version of microcode. Online the new cpus i did find the microcode was updated 
during online process.

Since offline ones don't participate in any OS activity  thought its ok to 
update everything that is available and visitible to the OS.

If BIOS has turned off cores due to some failures and didn't expose
in MADT during boot, we will never get a chance to update online.

> > -		tmp_ret = reload_for_cpu(cpu);
> > +		tmp_ret = microcode_ops->request_microcode_fw(cpu,
> > +				&microcode_pdev->dev, true);
> 
> This needs to happen only once - not per CPU. Let's simply forget
> heterogeneous microcode revisions.

Sounds good.. let me take a look at this.

> 
> >  		if (tmp_ret > UCODE_NFOUND) {
> > -			pr_warn("Error reloading microcode on CPU %d\n", cpu);
> > +			pr_warn("Error reloading microcode file for CPU %d\n", cpu);
> >  
> >  			/* set retval for the first encountered reload error */
> >  			if (!ret)
> >  				ret = -EINVAL;
> 
> You can't continue loading here if you've encountered an error.

Sounds good.
> 
> >  		}
> > -
> > -		if (tmp_ret == UCODE_UPDATED)
> > -			do_callback = true;
> >  	}
> > +	pr_debug("Done loading microcode file for all cpus\n");
> >  
> > -	if (!ret && do_callback)
> > +	memset(&uc_data, 0, sizeof(struct ucode_update_param));
> > +	spin_lock_init(&uc_data.ucode_lock);
> > +	atomic_set(&uc_data.enter, num_online_cpus());
> > +	/*
> > +	 * Wait for a 1 sec
> > +	 */
> > +	uc_data.timeout = USEC_PER_SEC;
> > +	stop_machine(ucode_load_rendezvous, &uc_data, cpu_online_mask);
> > +
> > +	pr_debug("Total CPUS = %d uperrors = %d\n",
> > +		atomic_read(&uc_data.count), atomic_read(&uc_data.errors));
> > +
> > +	if (atomic_read(&uc_data.errors))
> > +		pr_warn("Update failed for %d cpus\n", atomic_read(&uc_data.errors));
> > +	else
> >  		microcode_check();
> 
> This whole jumping through hoops needs to be extracted away in a
> separate function.

Not sure what you mean by jumping through hoops need to be extracted away.. 

> 
> Ok, that should be enough review for now. More with v2.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
> --