linux-kernel - [PATCH] x86/mm: Unbreak modules that rely on external PAGE

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Date:   Wed, 8 Nov 2017 21:18:18 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: [PATCH] x86/mm: Unbreak modules that rely on external PAGE_KERNEL
 availability

From: Jiri Kosina <jkosina@...e.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.

Cc: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
---
 arch/x86/mm/mem_encrypt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 16c5f37933a2..0286327e65fa 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -40,7 +40,7 @@ static char sme_cmdline_off[] __initdata = "off";
  * section is later cleared.
  */
 u64 sme_me_mask __section(.data) = 0;
-EXPORT_SYMBOL_GPL(sme_me_mask);
+EXPORT_SYMBOL(sme_me_mask);

 /* Buffer used for early in-place encryption by BSP, no locking needed */
 static char sme_early_buffer[PAGE_SIZE] __aligned(PAGE_SIZE);

-- 
Jiri Kosina
SUSE Labs