linux-kernel - Re: [PATCH v4 3/7] x86: put msr-index.h in uapi

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Message-ID: <3d68da69-353d-2fd0-ee1d-6ec3a0285607@6wind.com>
Date:   Tue, 31 Jan 2017 11:58:57 +0100
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Borislav Petkov <bp@...en8.de>
Cc:     arnd@...db.de, mmarek@...e.com, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        airlied@...ux.ie, davem@...emloft.net, slash.tmp@...e.fr,
        daniel.vetter@...ll.ch, msalter@...hat.com, jengelh@...i.de,
        hch@...radead.org, tklauser@...tanz.ch, mpe@...erman.id.au,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v4 3/7] x86: put msr-index.h in uapi

Le 30/01/2017 à 15:51, Russell King - ARM Linux a écrit :
> On Mon, Jan 23, 2017 at 05:52:45PM +0100, Borislav Petkov wrote:
>> On Mon, Jan 23, 2017 at 03:58:37PM +0100, Nicolas Dichtel wrote:
>>> This header file is exported, thus move it to uapi.
>>
>> Why? Why is this damn thing exported in the first place?
>>
>> The moment we decide to change an MSR name or even remove it from that
>> file, we break userspace. And what for, because userspace is using some
>> arbitrary header file which was meant to be for the kernel solely.
>>
>> NAKed-by: Borislav Petkov <bp@...e.de>
> 
> Here on my Fedora system:
> 
> $ less /usr/include/asm/msr-index.h
> #ifndef _ASM_X86_MSR_INDEX_H
> #define _ASM_X86_MSR_INDEX_H
> 
> /* CPU model specific register (MSR) numbers */
> 
> /* x86-64 specific MSRs */
> #define MSR_EFER                0xc0000080 /* extended feature register */
> #define MSR_STAR                0xc0000081 /* legacy mode SYSCALL target */
> #define MSR_LSTAR               0xc0000082 /* long mode SYSCALL target */
> ...
> 
> Like it or not, it is _already_ exported to userspace, so it forms
> part of the user ABI.  You can try to remove it from userspace view,
> but if anyone has already started to use it, removing it will already
> cause a userspace regression.
> 
> So, I don't think we have any grounds to NAK these patches on the
> basis of "we don't want this to be visible to userspace because it
> may cause a userspace regression."  Removing it from userspace view
> is likely to cause a userspace regression.
> 
> This patch just makes sure that such a regression doesn't happen when
> kbuild stops exporting files in _non_-uapi directories.
Yes, it was the only goal. My patch changes nothing!
Is it possible to find a consensus about this patch?
Ingo ?