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Date: Wed, 8 Nov 2017 21:47:45 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86/mm: Unbreak modules that rely on external PAGE_KERNEL
 availability
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To: Jiri Kosina <jikos@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Tom Lendacky <thomas.lendacky@amd.com>, Borislav Petkov <bp@suse.de>, Linus Torvalds <torvalds@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, x86@kernel.org, Greg KH <greg@kroah.com>

On Wed, 8 Nov 2017, Jiri Kosina wrote:

> From: Jiri Kosina <jkosina@suse.cz>
> 
> Commit
> 
>   7744ccdbc16f0 ("x86/mm: Add Secure Memory Encryption (SME) support")
> 
> as a side-effect made PAGE_KERNEL all of a sudden unavailable to modules 
> which can't make use of EXPORT_SYMBOL_GPL() symbols.
> 
> This is because once SME is enabled, sme_me_mask (which is introduced as 
> EXPORT_SYMBOL_GPL) makes its way to PAGE_KERNEL through _PAGE_ENC, causing 
> imminent build failure for all the modules which make use of all the 
> EXPORT-SYMBOL()-exported API (such as vmap(), __vmalloc(), 
> remap_pfn_range(), ...).
> 
> Exporting (as EXPORT_SYMBOL()) interfaces (and having done so for ages) 
> that take pgprot_t argument, while making it impossible to -- all of a 
> sudden -- pass PAGE_KERNEL to it, feels rather incosistent.
> 
> Restore the original behavior and make it possible to pass PAGE_KERNEL to 
> all its EXPORT_SYMBOL() consumers.

To be honest, I fundamentaly hate this, because proprietary crap out there
more or less holds the kernel hostage in its decisions of marking new
functionality GPL only. You have already a choice by disabling SME, but
sure you want to get everything: new features and proprietary stuff.

I fear, that I can't prevent this from being applied, but whoever picks up
that patch, please add:

Despised-by: Thomas Gleixner <tglx@linutronix.de>

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