linux-kernel - Re: [PATCH] x86: Remove the arch_calc_vm_prot

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Message-Id: <9b13c279-a667-4110-8cb6-01721d335c33@app.fastmail.com>
Date:   Thu, 06 Jul 2023 22:36:40 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Dave Hansen" <dave.hansen@...el.com>,
        "Thomas Huth" <thuth@...hat.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Nicolas Schier" <nicolas@...sle.eu>,
        "Masahiro Yamada" <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Remove the arch_calc_vm_prot_bits() macro from the uapi

On Thu, Jul 6, 2023, at 22:30, Dave Hansen wrote:
> On 7/6/23 13:22, Arnd Bergmann wrote:
>> On Thu, Jul 6, 2023, at 21:02, Thomas Huth wrote:
>>> The arch_calc_vm_prot_bits() macro uses VM_PKEY_BIT0 etc. which are
>>> not part of the uapi, so the macro is completely useless for userspace.
>>> It is also hidden behind the CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
>>> config switch which we shouldn't expose to userspace. Thus let's move
>>> this macro into a new internal header instead.
>>>
>>> Signed-off-by: Thomas Huth <thuth@...hat.com>
>> Fixes: 8f62c883222c9 ("x86/mm/pkeys: Add arch-specific VMA protection bits")
>> Reviewed-by: Arnd Bergmann <arnd@...db.de>
>> 
>> It looks like this was introduced right after the uapi split,
>> and probably is the result of an incorrect rebase.
>
> Yeah, I bet I just glossed over the "uapi" in the path.
>
> Is this causing any real problems?  Or is it OK to just send it along
> during the next merge window with other random cleanups?

It's pretty harmless, there are currently 12 remaining CONFIG_*
#ifdef checks in uapi headers, which scripts/headers_install.sh
has an exception for, and unlike some of the others, this one has
no relevance for the actual uapi.

Ultimately, the goal is to remove the list of known instances
from the script and just warn about all of them when new ones
get added, but it only becomes urgent when we get to everything
else.

     Arnd