[tip:x86/pti] x86/pti: Make sure the user/kernel PTEs match

[tip-bot for Thomas Gleixner <tipbot@zytor.com>]

Commit-ID:  52994c256df36fda9a715697431cba9daecb6b11
Gitweb:     https://git.kernel.org/tip/52994c256df36fda9a715697431cba9daecb6b11
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 3 Jan 2018 15:57:59 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 3 Jan 2018 15:57:59 +0100

x86/pti: Make sure the user/kernel PTEs match

Meelis reported that his K8 Athlon64 emits MCE warnings when PTI is
enabled:

[Hardware Error]: Error Addr: 0x0000ffff81e000e0
[Hardware Error]: MC1 Error: L1 TLB multimatch.
[Hardware Error]: cache level: L1, tx: INSN

The address is in the entry area, which is mapped into kernel _AND_ user
space. That's special because we switch CR3 while we are executing
there. 

User mapping:
0xffffffff81e00000-0xffffffff82000000           2M     ro         PSE     GLB x  pmd

Kernel mapping:
0xffffffff81000000-0xffffffff82000000          16M     ro         PSE         x  pmd

So the K8 is complaining that the TLB entries differ. They differ in the
GLB bit.

Drop the GLB bit when installing the user shared mapping.

Fixes: 6dc72c3cbca0 ("x86/mm/pti: Share entry text PMD")
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Meelis Roos <mroos@linux.ee>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801031407180.1957@nanos
---
 arch/x86/mm/pti.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index bce8aea..2da28ba 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -367,7 +367,8 @@ static void __init pti_setup_espfix64(void)
 static void __init pti_clone_entry_text(void)
 {
 	pti_clone_pmds((unsigned long) __entry_text_start,
-			(unsigned long) __irqentry_text_end, _PAGE_RW);
+			(unsigned long) __irqentry_text_end,
+		       _PAGE_RW | _PAGE_GLOBAL);
 }
 
 /*