linux-kernel - Re: [PATCH 05/17] virt: acrn: Introduce ACRN HSM basic driver

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Message-ID: <20200829104612.GD13723@shuo-intel.sh.intel.com>
Date:   Sat, 29 Aug 2020 18:46:12 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     <linux-kernel@...r.kernel.org>, "H . Peter Anvin" <hpa@...or.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Borislav Petkov" <bp@...en8.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>, <x86@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH 05/17] virt: acrn: Introduce ACRN HSM basic driver

Hi Greg,

On Fri 28.Aug'20 at 12:25:59 +0200, Greg Kroah-Hartman wrote:
>On Tue, Aug 25, 2020 at 10:45:05AM +0800, shuo.a.liu@...el.com wrote:
>> +static long acrn_dev_ioctl(struct file *filp, unsigned int cmd,
>> +			   unsigned long ioctl_param)
>> +{
>> +	if (cmd == ACRN_IOCTL_GET_API_VERSION) {
>> +		if (copy_to_user((void __user *)ioctl_param,
>> +				 &api_version, sizeof(api_version)))
>> +			return -EFAULT;
>
>Why are you versioning your api?  Shouldn't that not be a thing and you
>either support an ioctl or you do not?

The API version here is more for the hypercalls.
The hypercalls might evolve later and the version indicates which set of
interfaces (include the paramters' format) should be used by user space
tools. Currently, it's used rarely.

>
>
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int acrn_dev_release(struct inode *inode, struct file *filp)
>> +{
>> +	struct acrn_vm *vm = filp->private_data;
>> +
>> +	kfree(vm);
>> +	return 0;
>> +}
>> +
>> +static const struct file_operations acrn_fops = {
>> +	.owner		= THIS_MODULE,
>> +	.open		= acrn_dev_open,
>> +	.release	= acrn_dev_release,
>> +	.unlocked_ioctl	= acrn_dev_ioctl,
>> +};
>> +
>> +static struct miscdevice acrn_dev = {
>> +	.minor	= MISC_DYNAMIC_MINOR,
>> +	.name	= "acrn_hsm",
>> +	.fops	= &acrn_fops,
>> +};
>> +
>> +static int __init hsm_init(void)
>> +{
>> +	int ret;
>> +
>> +	if (x86_hyper_type != X86_HYPER_ACRN)
>> +		return -ENODEV;
>> +
>> +	if (!acrn_is_privileged_vm())
>> +		return -EPERM;
>> +
>> +	ret = hcall_get_api_version(slow_virt_to_phys(&api_version));
>> +	if (ret < 0) {
>> +		pr_err("Failed to get API version from hypervisor!\n");
>> +		return ret;
>> +	}
>> +
>> +	pr_info("API version is %u.%u\n",
>> +		api_version.major_version, api_version.minor_version);
>
>Shouldn't drivers be quiet when they load and all goes well?  pr_dbg()?
>
>And can't you defer the "read the version" call until open happens?
>Does it have to happen at module load time, increasing boot time for no
>good reason if there is not a user?

OK. I can defer the version fetch and pr_dbg() until open.

Thanks
shuo