linux-kernel - Re: [PATCH v1 2/3] virt: tdx-guest: Add Quote generation support

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Date:   Sun, 26 Mar 2023 08:34:53 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Guorui Yu <GuoRui.Yu@...ux.alibaba.com>,
        Du Fan <fan.du@...el.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v1 2/3] virt: tdx-guest: Add Quote generation support

On Sat, Mar 25, 2023 at 11:20:38PM -0700, Kuppuswamy Sathyanarayanan wrote:
> Since GetQuote support requires usage of DMA APIs, convert TDX guest
> driver to a platform driver.

Sorry, but that's not a valid reason to use a platform device for fake
things like this:

> +static struct platform_device *tdx_dev;

Especially a single static one.

> +static int tdx_guest_probe(struct platform_device *pdev)
> +{
> +	if (tdx_register_event_irq_cb(attestation_callback_handler, pdev))
> +		return -EIO;
> +
> +	return misc_register(&tdx_misc_dev);
> +}
> +
> +static int tdx_guest_remove(struct platform_device *pdev)
> +{
> +	tdx_unregister_event_irq_cb(attestation_callback_handler, pdev);
> +	misc_deregister(&tdx_misc_dev);
> +	return 0;
> +}
> +
> +static struct platform_driver tdx_guest_driver = {
> +	.probe = tdx_guest_probe,
> +	.remove = tdx_guest_remove,
> +	.driver.name = KBUILD_MODNAME,
> +};
> +
>  static const struct x86_cpu_id tdx_guest_ids[] = {
>  	X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
>  	{}
> @@ -84,16 +310,35 @@ MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
>  
>  static int __init tdx_guest_init(void)
>  {
> +	int ret;
> +
>  	if (!x86_match_cpu(tdx_guest_ids))
>  		return -ENODEV;
>  
> -	return misc_register(&tdx_misc_dev);
> +	ret = platform_driver_register(&tdx_guest_driver);
> +	if (ret) {
> +		pr_err("failed to register driver, err=%d\n", ret);
> +		return ret;
> +	}

No, please do not create a fake platform driver.

> +	tdx_dev = platform_device_register_simple(KBUILD_MODNAME,
> +						  PLATFORM_DEVID_NONE,
> +						  NULL, 0);

And please do not create a fake platform device.

As always, do not create fake platform devices for things that are NOT
platform devices.

If this device needs DMA (but why?) then make it a real device and tie
it to the bus it belongs to (that it is obviously doing DMA on.)

But as-is, this isn't ok, sorry.

thanks,

greg k-h