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

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Date:   Tue, 22 Mar 2022 14:11:44 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "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

Hi Michael,

On 3/22/22, Michael Kelley (LINUX) <mikelley@...rosoft.com> wrote:
> From: Ard Biesheuvel <ardb@...nel.org> Sent: Monday, February 28, 2022 2:47
> PM
>>
>> On Mon, 28 Feb 2022 at 23:38, Michael Kelley (LINUX)
>> <mikelley@...rosoft.com> wrote:
>> >
>> > From: Ard Biesheuvel <ardb@...nel.org> Sent: Monday, February 28, 2022
>> > 2:22 PM
>> > >
>> > > On Mon, 28 Feb 2022 at 23:14, Michael Kelley (LINUX)
>> > > <mikelley@...rosoft.com> wrote:
>> > > >
>> > > > 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.
>> > > >
>> > >
>> > > Thanks for chiming in.
>> > >
>> > > Why not do something like
>> > >
>> > > Name (_CID, Package (2) { "VM_GEN_COUNTER", "VMGENCTR" } )
>> > >
>> > > ?
>> > >
>> > > That way, older clients can match on the existing _CID and new
>> > > clients
>> > > can match on the spec compliant one.
>> >
>> > I'll run this by the Hyper-V guys.  I don't have the ACPI expertise to
>> > disagree
>> > with them when they say they can't change it. :-(
>> >
>>
>> Yes, please, even if it makes no difference for this particular patch.
>
> The Hyper-V guys pass along their thanks for your suggestion.  They have
> created an internal build with the change and verified that it preserves
> compatibility with Windows guests.  I've tested with Linux guests and
> Jason's new driver (modified to look for "VMGENCTR"), and it all looks
> good.
> It will take a little while to wend its way through the Windows/Hyper-V
> release system, but they are planning to take the change.
>
> Michael
>

Do you want to send a patch against the crng/random.git tree adding that new id?

Jason