Patch "x86/pgtable: Don't set huge PUD/PMD on non-leaf entries" has been added to the 4.16-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-pgtable-don-t-set-huge-pud-pmd-on-non-leaf-entries.patch
and it can be found in the queue-4.16 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Joerg Roedel <[email protected]>
Date: Wed, 11 Apr 2018 17:24:38 +0200
Subject: x86/pgtable: Don't set huge PUD/PMD on non-leaf entries

From: Joerg Roedel <[email protected]>

[ Upstream commit e3e288121408c3abeed5af60b87b95c847143845 ]

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.

---
 arch/x86/mm/pgtable.c |    9 +++++++++
 1 file changed, 9 insertions(+)

@@ -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>

@@ -636,6 +637,10 @@ int pud_set_huge(pud_t *pud, phys_addr_t
 	    (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(

@@ -664,6 +669,10 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t
 		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(

Patches currently in stable-queue which might be from [email protected] are

queue-4.16/x86-apic-set-up-through-local-apic-mode-on-the-boot-cpu-if-noapic-specified.patch queue-4.16/x86-pgtable-don-t-set-huge-pud-pmd-on-non-leaf-entries.patch