Date:   Thu, 23 Sep 2021 00:33:21 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Aubrey Li <aubrey.li@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Hans de Goede <hdegoede@...hat.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 3/5] drivers/acpi: Introduce Platform Firmware Runtime
 Update device driver

On Wed, Sep 22, 2021 at 11:10:02AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Sep 22, 2021 at 05:04:42PM +0800, Chen Yu wrote:
> > Hi Greg,
> > On Tue, Sep 21, 2021 at 05:59:05PM +0200, Greg Kroah-Hartman wrote:
> > > On Fri, Sep 17, 2021 at 12:02:18AM +0800, Chen Yu wrote:
> > > > Introduce the pfru_update driver which can be used for Platform Firmware
> > > > Runtime code injection and driver update. The user is expected to provide
> > > > the update firmware in the form of capsule file, and pass it to the driver
> > > > via ioctl. Then the driver would hand this capsule file to the Platform
> > > > Firmware Runtime Update via the ACPI device _DSM method. At last the low
> > > > level Management Mode would do the firmware update.
> > > > 
> > > > Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> > > 
> > > Where is the userspace code that uses this ioctl and has tested it out
> > > to verify it works properly?  A link to that in the changelog would be
> > > great to have.
> > > 
> > The patch [5/5] is a self testing tool to test the whole feature. I'll send a
> > new version and Cc you too.
> 
> That tests it, but does not answer the question of who will actually use
> this.  What userspace tool needs this new api?
>
One end user is the cloud user. Currently there is no dedicated userspace
tool developed to use this feature AFAIK. It was expected that the end users
could refer to the self test tool to customize their tools. I'm not sure if
this is the proper way to propose the feature, may I have your suggestion on
this, should I create a separate git repository for this tool, or put it in
tools/selftestings as it is now?
> > > > +static void dump_update_result(struct pfru_updated_result *result)
> > > > +{
> > > > +	pr_debug("Update result:\n");
> > > > +	pr_debug("Status:%d\n", result->status);
> > > > +	pr_debug("Extended Status:%d\n", result->ext_status);
> > > > +	pr_debug("Authentication Time Low:%lld\n", result->low_auth_time);
> > > > +	pr_debug("Authentication Time High:%lld\n", result->high_auth_time);
> > > > +	pr_debug("Execution Time Low:%lld\n", result->low_exec_time);
> > > > +	pr_debug("Execution Time High:%lld\n", result->high_exec_time);
> > > 
> > > Why not dev_dbg()?  Same for all pr_* calls in this "driver".
> > > 
> > >
> > Ok, I'll switch to dev_dbg() in next version. 
> > > > +static long pfru_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > > > +{
> > > > +	void __user *p;
> > > > +	int ret = 0, rev;
> > > > +
> > > > +	p = (void __user *)arg;
> > > > +
> > > > +	switch (cmd) {
> > > > +	case PFRU_IOC_SET_REV:
> > > > +		if (copy_from_user(&rev, p, sizeof(unsigned int)))
> > > > +			return -EFAULT;
> > > > +		if (!pfru_valid_revid(rev))
> > > > +			return -EFAULT;
> > > > +		pfru_dev->rev_id = rev;
> > > > +		break;
> > > > +	case PFRU_IOC_STAGE:
> > > > +		ret = start_acpi_update(START_STAGE);
> > > > +		break;
> > > > +	case PFRU_IOC_ACTIVATE:
> > > > +		ret = start_acpi_update(START_ACTIVATE);
> > > > +		break;
> > > > +	case PFRU_IOC_STAGE_ACTIVATE:
> > > > +		ret = start_acpi_update(START_STAGE_ACTIVATE);
> > > > +		break;
> > > > +	default:
> > > > +		ret = -ENOIOCTLCMD;
> > > 
> > > Wrong value :(
> > Previously I thought that ENOIOCTLCMD stands for 'invalid ioctl command'.
> > After checking the lkml discussion, it seems that ENOIOCTLCMD should not
> > be returned to user space. ENOTTY might be more suitible if I understand
> > correctly.
> > http://lkml.iu.edu/hypermail/linux/kernel/0105.1/0734.html
> 
> Yes, ENOTTY is correct.
> 
>
> > > > +		break;
> > > > +	}
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +#ifdef CONFIG_COMPAT
> > > > +static long compat_pfru_ioctl(struct file *filep, unsigned int cmd,
> > > > +			      unsigned long arg)
> > > > +{
> > > > +	return pfru_ioctl(filep, cmd, arg);
> > > > +}
> > > > +#endif
> > > 
> > > Why is this compat ioctl needed at all?
> > > 
> > We can not control if the user space tool would be compiled as 32bit.
> 
> Then create your ioctl so that a compat ioctl is not needed at all.
> There is no need to ever use this for new ioctl commands these days.
> 
After checking the code, it seems that this driver only needs to deal with
unlocked_ioctl() without touching compat_ioctl(). Because even if the user
space is 32bit, the compat_ioctl() would invoke unlocked_ioctl() first
with a parameter of compat_ptr(arg). It should be safe to remove the compat_ioctl
hook in this driver.
> > But I realize that a compat_ptr() was missing. Will fix it in next version.
> > > > +static struct miscdevice pfru_misc_dev = {
> > > > +	.minor = MISC_DYNAMIC_MINOR,
> > > > +	.name = "pfru_update",
> > > > +	.nodename = "pfru/update",
> > > 
> > > Why is this in a subdirectory?  What requires this?  Why not just
> > > "pfru"?
> > > 
> > The pfru directory might be reused for pfru_telemetry device, whose driver
> > is in 4/5 patch, I'll Cc you with the whole patch set in next version.
> 
> "might be" is not a valid reason.  Why does this simple driver deserve a
> whole /dev/ subdirectory?
> 
There are pfru_update and pfru_telemetry in the patch, and there is plan to
add a pfru_prm device in the future, which stands for "Platform Runtime Mechanism".
I'll move them to /dev/ in next version.

Thanks,
Chenyu

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