Re: [PATCH] vfio/type1: Cleanup remaining vaddr removal/update fragments

Steven Sistare
2022-12-09T19:53:02Z

On 12/9/2022 2:42 PM, Alex Williamson wrote:
> On Fri, 9 Dec 2022 13:40:29 -0500
> Steven Sistare <steven.sistare@oracle.com> wrote:
>
>> On 12/8/2022 11:40 AM, Alex Williamson wrote:
>>> On Thu, 8 Dec 2022 07:56:30 +0000
>>> "Tian, Kevin" <kevin.tian@intel.com> wrote:
>>>
>>>>> From: Alex Williamson <alex.williamson@redhat.com>
>>>>> Sent: Thursday, December 8, 2022 5:45 AM
>>>>>
>>>>> Fix several loose ends relative to reverting support for vaddr removal
>>>>> and update. Mark feature and ioctl flags as deprecated, restore local
>>>>> variable scope in pin pages, remove remaining support in the mapping
>>>>> code.
>>>>>
>>>>> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
>>>>> ---
>>>>>
>>>>> This applies on top of Steve's patch[1] to fully remove and deprecate
>>>>> this feature in the short term, following the same methodology we used
>>>>> for the v1 migration interface removal. The intention would be to pick
>>>>> Steve's patch and this follow-on for v6.2 given that existing support
>>>>> exposes vulnerabilities and no known upstream userspaces make use of
>>>>> this feature.
>>>>>
>>>>> [1]https://lore.kernel.org/all/1670363753-249738-2-git-send-email-
>>>>> steven.sistare@oracle.com/
>>>>>
>>>>
>>>> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
>>>>
>>>> btw given the exposure and no known upstream usage should this be
>>>> also pushed to stable kernels?
>>>
>>> I'll add to both:
>>>
>>> Cc: stable@vger.kernel.org # v5.12+
>>
>> We maintain and use a version of qemu that contains the live update patches,
>> and requires these kernel interfaces. Other companies are also experimenting
>> with it. Please do not remove it from stable.
>
> The interface has been determined to have vulnerabilities and the
> proposal to resolve those vulnerabilities is to implement a new API.
> If we think it's worthwhile to remove the existing, vulnerable interface
> in the current kernel, what makes it safe to keep it for stable kernels?

I do not think it's worth while, but I have stopped fighting for 6.2.

> Existing users that could choose not to accept the revert in their
> downstream kernel and allowing users evaluating the interface more time
> before they know it's been removed upstream, are not terribly
> compelling reasons to keep it in upstream stable kernels. Thanks,

The compelling reason is that stable is supposed to be stable and maintain
existing interfaces, and now I will need to re-merge the interfaces at
regular intervals when we update UEK from stable. Oracle is a current user
of these interfaces in our business. Do we count?

- Steve