linux-kernel - Re: [PATCH] platform/x86/amd/hsmp: mark hsmp_msg_desc_table[] as maybe

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Message-Id: <a3b3aa23-3238-4117-b931-7194fc1ccc34@app.fastmail.com>
Date: Wed, 30 Oct 2024 14:19:18 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Hans de Goede" <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 "Arnd Bergmann" <arnd@...nel.org>, "Suma Hegde" <suma.hegde@....com>
Cc: "Naveen Krishna Chatradhi" <naveenkrishna.chatradhi@....com>,
 "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,
 "Carlos Bilbao" <carlos.bilbao.osdev@...il.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Randy Dunlap" <rdunlap@...radead.org>,
 "Bjorn Helgaas" <bhelgaas@...gle.com>, platform-driver-x86@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] platform/x86/amd/hsmp: mark hsmp_msg_desc_table[] as maybe_unused

On Wed, Oct 30, 2024, at 14:16, Hans de Goede wrote:
> On 29-Oct-24 1:55 PM, Ilpo Järvinen wrote:
>> On Mon, 28 Oct 2024, Arnd Bergmann wrote:
>> 
>> It seems that the main goal why it was put into UAPI was "to give the user 
>> some reference about proper num_args and response_size for each message":
>> 
>> https://lore.kernel.org/all/CAPhsuW5V0BJT+YSwv1U=hRG0k9zBWXeRd=E1n4U5hvcnwEV3mQ@mail.gmail.com/
>> 
>> Are we actually expecting userspace to benefit from this in C form?
>> Suma? Hans?
>
> I can see how having this available in the uapi header as documentation
> of sorts is somewhat useful.
>
> OTOH I do agree that this array should probably not be used by userspace.
>
> And there is only 1 way to find out if it is actually used (which I do not
> expect) and that is to just drop it and find out (and to be willing to
> revert the change if it breaks things).
>
> So we can either move the array in its entirety to the c-code consuming it,
> which I think would be best; or we can go with Arnd's patch + add
>
> #ifdef __KERNEL__ 
>
> around the array so that it is there for people reading the header, but
> it is no longer exposed as uapi.
>

I don't think that would work, because the 'make headers_install'
step just removes the contents of #ifdef __KERNEL__, in this case
you just end up with a uapi header that doesn't have the array.

      Arnd