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SubjectRe: CONFIG_PAGE_TABLE_ISOLATION=y on x86_64 causes gcc to segfault when building x86_32 binaries
On Wed, 3 Jan 2018, Lars Wendler wrote:
> Am Wed, 3 Jan 2018 13:05:38 +0100 (CET)
> schrieb Thomas Gleixner <tglx@linutronix.de>:
> > Also can you please try Linus v4.15-rc6 with PTI enabled so we can see
> > whether that's a backport issue or a general one?
>
> Same problem with 4.15-rc6. So I suppose that means it's a general
> issue.

Just a shot in the dark as I just decoded another issue on a AMD CPU. Can
you please try the patch below?

Thanks,

tglx

8<---------------

commit 52994c256df36fda9a715697431cba9daecb6b11
Author: Thomas Gleixner <tglx@linutronix.de>
Date: Wed Jan 3 15:57:59 2018 +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

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index bce8aea65606..2da28ba97508 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);
}

/*
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