linux-kernel - RE: [PATCH 2/3 v6] ACPI: allow longer device IDs

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Message-ID: <MN0PR21MB3098981B77F513976A62CA57D7019@MN0PR21MB3098.namprd21.prod.outlook.com>
Date:   Mon, 28 Feb 2022 22:14:52 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     jason <jason@...c4.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Ard Biesheuvel <ardb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Alexander Graf <graf@...zon.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: RE: [PATCH 2/3 v6] ACPI: allow longer device IDs

From: Jason A. Donenfeld <Jason@...c4.com> Sent: Monday, February 28, 2022 1:55 PM
> 
> Hi Andy,
> 
> On Mon, Feb 28, 2022 at 10:28 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > My point is that this is clear abuse of the spec and:
> > 1) we have to enable the broken, because it is already in the wild with
> >    the comment that this is an issue
> >
> > AND
> >
> > 2) issue an ECR / work with MS to make sure they understand the problem.
> >
> > This can be done in parallel. What I meant as a prerequisite is to start doing
> > 2) while we have 1) on table.
> 
> Oh, okay, that makes sense. If you want to get (2) going, by all means
> go for it. I have no idea how to do this myself; Ard said something
> about joining the UEFI forum as an individual something or another but
> I don't think I'm the man for the job there. Is this something that
> Intel can do with their existing membership (is that the right term?)
> at the UEFI forum? Or maybe a Microsoft engineer on the list?

My team at Microsoft, which works on Linux, filed a bug on this
issue against the Hyper-V team about a year ago, probably when the issue
was raised during the previous attempt to implement the functionality
in Linux.  I've talked with the Hyper-V dev manager, and they acknowledge
that the ACPI entry Hyper-V provides to guest VMs violates the spec.  But
changing to an identifier that meets the spec is problematic because
of backwards compatibility with Windows guests on Hyper-V that
consume the current identifier.  There's no practical way to have Hyper-V
provide a conformant identifier AND fix all the Windows guests out in
the wild to consume the new identifier.   As a result, at this point Hyper-V
is not planning to change anything.

It's a lousy state-of-affairs, but as mentioned previously in this thread,
it seems to be one that we will have to live with.

Michael

> 
> From my side, regarding (1), I'm basically just waiting for Rafael's
> "Acked-by" (or an explicit nack) so I can put this in my tree and move
> on.
> 
> Jason