linux-kernel - Re: [PATCH v5 5/6] dcdbas: make use of smp_call_on

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Date:	Wed, 15 Jun 2016 13:19:29 +0200
From:	Juergen Gross <jgross@...e.com>
To:	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:	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, linux@...ck-us.net,
	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 v5 5/6] dcdbas: make use of smp_call_on_cpu()

On 06/04/16 16:17, Juergen Gross wrote:
> Use smp_call_on_cpu() to raise SMI 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>

Could please some maintainer comment on this patch?


Juergen

> ---
> V4: add call to get_online_cpus()
> ---
>   drivers/firmware/dcdbas.c | 51 ++++++++++++++++++++++++-----------------------
>   1 file changed, 26 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
> index 829eec8..2fe1a13 100644
> --- a/drivers/firmware/dcdbas.c
> +++ b/drivers/firmware/dcdbas.c
> @@ -23,6 +23,7 @@
>   #include <linux/platform_device.h>
>   #include <linux/dma-mapping.h>
>   #include <linux/errno.h>
> +#include <linux/cpu.h>
>   #include <linux/gfp.h>
>   #include <linux/init.h>
>   #include <linux/kernel.h>
> @@ -238,33 +239,14 @@ static ssize_t host_control_on_shutdown_store(struct device *dev,
>   	return count;
>   }
>
> -/**
> - * dcdbas_smi_request: generate SMI request
> - *
> - * Called with smi_data_lock.
> - */
> -int dcdbas_smi_request(struct smi_cmd *smi_cmd)
> +static int raise_smi(void *par)
>   {
> -	cpumask_var_t old_mask;
> -	int ret = 0;
> +	struct smi_cmd *smi_cmd = par;
>
> -	if (smi_cmd->magic != SMI_CMD_MAGIC) {
> -		dev_info(&dcdbas_pdev->dev, "%s: invalid magic value\n",
> -			 __func__);
> -		return -EBADR;
> -	}
> -
> -	/* SMI requires CPU 0 */
> -	if (!alloc_cpumask_var(&old_mask, GFP_KERNEL))
> -		return -ENOMEM;
> -
> -	cpumask_copy(old_mask, &current->cpus_allowed);
> -	set_cpus_allowed_ptr(current, cpumask_of(0));
>   	if (smp_processor_id() != 0) {
>   		dev_dbg(&dcdbas_pdev->dev, "%s: failed to get CPU 0\n",
>   			__func__);
> -		ret = -EBUSY;
> -		goto out;
> +		return -EBUSY;
>   	}
>
>   	/* generate SMI */
> @@ -280,9 +262,28 @@ int dcdbas_smi_request(struct smi_cmd *smi_cmd)
>   		: "memory"
>   	);
>
> -out:
> -	set_cpus_allowed_ptr(current, old_mask);
> -	free_cpumask_var(old_mask);
> +	return 0;
> +}
> +/**
> + * dcdbas_smi_request: generate SMI request
> + *
> + * Called with smi_data_lock.
> + */
> +int dcdbas_smi_request(struct smi_cmd *smi_cmd)
> +{
> +	int ret;
> +
> +	if (smi_cmd->magic != SMI_CMD_MAGIC) {
> +		dev_info(&dcdbas_pdev->dev, "%s: invalid magic value\n",
> +			 __func__);
> +		return -EBADR;
> +	}
> +
> +	/* SMI requires CPU 0 */
> +	get_online_cpus();
> +	ret = smp_call_on_cpu(0, raise_smi, smi_cmd, true);
> +	put_online_cpus();
> +
>   	return ret;
>   }
>
>