linux-kernel - Re: [PATCH v4 6/6] hwmon: use smp_call_on

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Date:	Tue, 5 Apr 2016 07:54:14 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Juergen Gross <jgross@...e.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	mingo@...hat.com, peterz@...radead.org, Douglas_Warzecha@...l.com,
	pali.rohar@...il.com, jdelvare@...e.com, tglx@...utronix.de,
	hpa@...or.com, jeremy@...p.org, chrisw@...s-sol.org,
	akataria@...are.com, rusty@...tcorp.com.au,
	virtualization@...ts.linux-foundation.org, x86@...nel.org
Subject: Re: [PATCH v4 6/6] hwmon: use smp_call_on_cpu() for dell-smm i8k

On Tue, Apr 05, 2016 at 07:10:07AM +0200, Juergen Gross wrote:
> Use the smp_call_on_cpu() function to call system management
> mode on cpu 0.
> Make call secure by adding get_online_cpus() to avoid e.g. suspend
> resume cycles in between.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> V4: add call to get_online_cpus()

Pali, any chance to test this ?

Thanks,
Guenter

> ---
>  drivers/hwmon/dell-smm-hwmon.c | 35 ++++++++++++++++++++---------------
>  1 file changed, 20 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index c43318d..643f3a1 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -21,6 +21,7 @@
>  
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
> +#include <linux/cpu.h>
>  #include <linux/delay.h>
>  #include <linux/module.h>
>  #include <linux/types.h>
> @@ -35,6 +36,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/io.h>
>  #include <linux/sched.h>
> +#include <linux/smp.h>
>  
>  #include <linux/i8k.h>
>  
> @@ -130,23 +132,15 @@ static inline const char *i8k_get_dmi_data(int field)
>  /*
>   * Call the System Management Mode BIOS. Code provided by Jonathan Buzzard.
>   */
> -static int i8k_smm(struct smm_regs *regs)
> +static int i8k_smm_func(void *par)
>  {
>  	int rc;
> +	struct smm_regs *regs = par;
>  	int eax = regs->eax;
> -	cpumask_var_t old_mask;
>  
>  	/* SMM requires CPU 0 */
> -	if (!alloc_cpumask_var(&old_mask, GFP_KERNEL))
> -		return -ENOMEM;
> -	cpumask_copy(old_mask, &current->cpus_allowed);
> -	rc = set_cpus_allowed_ptr(current, cpumask_of(0));
> -	if (rc)
> -		goto out;
> -	if (smp_processor_id() != 0) {
> -		rc = -EBUSY;
> -		goto out;
> -	}
> +	if (smp_processor_id() != 0)
> +		return -EBUSY;
>  
>  #if defined(CONFIG_X86_64)
>  	asm volatile("pushq %%rax\n\t"
> @@ -204,13 +198,24 @@ static int i8k_smm(struct smm_regs *regs)
>  	if (rc != 0 || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
>  		rc = -EINVAL;
>  
> -out:
> -	set_cpus_allowed_ptr(current, old_mask);
> -	free_cpumask_var(old_mask);
>  	return rc;
>  }
>  
>  /*
> + * Call the System Management Mode BIOS.
> + */
> +static int i8k_smm(struct smm_regs *regs)
> +{
> +	int ret;
> +
> +	get_online_cpus();
> +	ret = smp_call_on_cpu(0, true, i8k_smm_func, regs);
> +	put_online_cpus();
> +
> +	return ret;
> +}
> +
> +/*
>   * Read the fan status.
>   */
>  static int i8k_get_fan_status(int fan)
> -- 
> 2.6.2
>