Commit e3e28812 authored Apr 11, 2018 by Joerg Roedel Committed by Ingo Molnar Apr 12, 2018

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@sympatico.ca>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <llong@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180411152437.GC15462@8bytes.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8c06c774

arch/x86/mm/pgtable.c

+9 −0

Original line number	Diff line number	Diff line
		// 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(

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