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Subject: Re: [PATCH v8] drivers/misc: sysgenid: add system generation id
 driver
To:     Greg KH <gregkh@linuxfoundation.org>,
        Adrian Catangiu <acatan@amazon.com>
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References: <1615213083-29869-1-git-send-email-acatan@amazon.com>
 <YEY2b1QU5RxozL0r@kroah.com>
From:   Alexander Graf <graf@amazon.com>
Message-ID: <a61c976f-b362-bb60-50a5-04073360e702@amazon.com>
Date:   Mon, 8 Mar 2021 17:03:58 +0100
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On 08.03.21 15:36, Greg KH wrote:
> =

> On Mon, Mar 08, 2021 at 04:18:03PM +0200, Adrian Catangiu wrote:
>> +static struct miscdevice sysgenid_misc =3D {
>> +     .minor =3D MISC_DYNAMIC_MINOR,
>> +     .name =3D "sysgenid",
>> +     .fops =3D &fops,
>> +};
> =

> Much cleaner, but:
> =

>> +static int __init sysgenid_init(void)
>> +{
>> +     int ret;
>> +
>> +     sysgenid_data.map_buf =3D get_zeroed_page(GFP_KERNEL);
>> +     if (!sysgenid_data.map_buf)
>> +             return -ENOMEM;
>> +
>> +     atomic_set(&sysgenid_data.generation_counter, 0);
>> +     atomic_set(&sysgenid_data.outdated_watchers, 0);
>> +     init_waitqueue_head(&sysgenid_data.read_waitq);
>> +     init_waitqueue_head(&sysgenid_data.outdated_waitq);
>> +     spin_lock_init(&sysgenid_data.lock);
>> +
>> +     ret =3D misc_register(&sysgenid_misc);
>> +     if (ret < 0) {
>> +             pr_err("misc_register() failed for sysgenid\n");
>> +             goto err;
>> +     }
>> +
>> +     return 0;
>> +
>> +err:
>> +     free_pages(sysgenid_data.map_buf, 0);
>> +     sysgenid_data.map_buf =3D 0;
>> +
>> +     return ret;
>> +}
>> +
>> +static void __exit sysgenid_exit(void)
>> +{
>> +     misc_deregister(&sysgenid_misc);
>> +     free_pages(sysgenid_data.map_buf, 0);
>> +     sysgenid_data.map_buf =3D 0;
>> +}
>> +
>> +module_init(sysgenid_init);
>> +module_exit(sysgenid_exit);
> =

> So you do this for any bit of hardware that happens to be out there?
> Will that really work?  You do not have any hwid to trigger off of to
> know that this is a valid device you can handle?

The interface is already useful in a pure container context where the =

generation change request is triggered by software.

And yes, there are hardware triggers, but Michael was quite unhappy =

about potential races between VMGenID change and SysGenID change and =

thus wanted to ideally separate the interfaces. So we went ahead and =

isolated the SysGenID one, as it's already useful as is.

Hardware drivers to inject change events into SysGenID can then follow =

later, for all different hardware platforms. But SysGenID as in this =

patch is a completely hardware agnostic concept.


Alex


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