linux-kernel - [tip:x86/pti] x86/pgtable: Don't set huge PUD/PMD on non-leaf entries

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Date:   Thu, 12 Apr 2018 00:52:23 -0700
From:   tip-bot for Joerg Roedel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        dhgutteridge@...patico.ca, llong@...hat.com,
        David.Laight@...lab.com, tglx@...utronix.de, dave.hansen@...el.com,
        jgross@...e.com, aarcange@...hat.com, brgerst@...il.com,
        jroedel@...e.de, jpoimboe@...hat.com, hpa@...or.com,
        torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
        will.deacon@....com, peterz@...radead.org, dvlasenk@...hat.com,
        boris.ostrovsky@...cle.com, luto@...nel.org, eduval@...zon.com,
        pavel@....cz, joro@...tes.org, bp@...en8.de, jkosina@...e.cz
Subject: [tip:x86/pti] x86/pgtable: Don't set huge PUD/PMD on non-leaf
 entries

Commit-ID:  e3e288121408c3abeed5af60b87b95c847143845
Gitweb:     https://git.kernel.org/tip/e3e288121408c3abeed5af60b87b95c847143845
Author:     Joerg Roedel <joro@...tes.org>
AuthorDate: Wed, 11 Apr 2018 17:24:38 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 12 Apr 2018 09:41:41 +0200

x86/pgtable: Don't set huge PUD/PMD on non-leaf entries

The pmd_set_huge() and pud_set_huge() functions are used from
the generic ioremap() code to establish large mappings where this
is possible.

But the generic ioremap() code does not check whether the
PMD/PUD entries are already populated with a non-leaf entry,
so that any page-table pages these entries point to will be
lost.

Further, on x86-32 with SHARED_KERNEL_PMD=0, this causes a
BUG_ON() in vmalloc_sync_one() when PMD entries are synced
from swapper_pg_dir to the current page-table. This happens
because the PMD entry from swapper_pg_dir was promoted to a
huge-page entry while the current PGD still contains the
non-leaf entry. Because both entries are present and point
to a different page, the BUG_ON() triggers.

This was actually triggered with pti-x32 enabled in a KVM
virtual machine by the graphics driver.

A real and better fix for that would be to improve the
page-table handling in the generic ioremap() code. But that is
out-of-scope for this patch-set and left for later work.

Reported-by: David H. Gutteridge <dhgutteridge@...patico.ca>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: David Laight <David.Laight@...lab.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Eduardo Valentin <eduval@...zon.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Pavel Machek <pavel@....cz>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Waiman Long <llong@...hat.com>
Cc: Will Deacon <will.deacon@....com>
Cc: aliguori@...zon.com
Cc: daniel.gruss@...k.tugraz.at
Cc: hughd@...gle.com
Cc: keescook@...gle.com
Cc: linux-mm@...ck.org
Link: http://lkml.kernel.org/r/20180411152437.GC15462@8bytes.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/pgtable.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index d10a40aceeaa..ffc8c13c50e4 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/mm.h>
 #include <linux/gfp.h>
+#include <linux/hugetlb.h>
 #include <asm/pgalloc.h>
 #include <asm/pgtable.h>
 #include <asm/tlb.h>
@@ -639,6 +640,10 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
 	    (mtrr != MTRR_TYPE_WRBACK))
 		return 0;
 
+	/* Bail out if we are we on a populated non-leaf entry: */
+	if (pud_present(*pud) && !pud_huge(*pud))
+		return 0;
+
 	prot = pgprot_4k_2_large(prot);
 
 	set_pte((pte_t *)pud, pfn_pte(
@@ -667,6 +672,10 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
 		return 0;
 	}
 
+	/* Bail out if we are we on a populated non-leaf entry: */
+	if (pmd_present(*pmd) && !pmd_huge(*pmd))
+		return 0;
+
 	prot = pgprot_4k_2_large(prot);
 
 	set_pte((pte_t *)pmd, pfn_pte(