[Xenomai] [PATCH] x86/mm: Fix vmalloc_fault() to handle large pages properly

Henning Schild henning.schild at siemens.com
Tue Feb 28 12:31:50 CET 2017

From: Toshi Kani <toshi.kani at hpe.com>

[ Upstream commit f4eafd8bcd5229e998aa252627703b8462c3b90f ]

A kernel page fault oops with the callstack below was observed
when a read syscall was made to a pmem device after a huge amount
(>512GB) of vmalloc ranges was allocated by ioremap() on a x86_64

     BUG: unable to handle kernel paging request at ffff880840000ff8
     IP: vmalloc_fault+0x1be/0x300
     PGD c7f03a067 PUD 0
     Oops: 0000 [#1] SM
     Call Trace:
        ? put_prev_entity+0x35/0x7a0
        ? memcpy_erms+0x6/0x10
        ? schedule+0x35/0x80
        ? pmem_rw_bytes+0x6a/0x190 [nd_pmem]
        ? schedule_timeout+0x183/0x240
        btt_log_read+0x63/0x140 [nd_btt]
        ? __symbol_put+0x60/0x60
        ? kernel_read+0x50/0x80

Since v4.1, ioremap() supports large page (pud/pmd) mappings in
x86_64 and PAE.  vmalloc_fault() however assumes that the vmalloc
range is limited to pte mappings.

vmalloc faults do not normally happen in ioremap'd ranges since
ioremap() sets up the kernel page tables, which are shared by
user processes.  pgd_ctor() sets the kernel's PGD entries to
user's during fork().  When allocation of the vmalloc ranges
crosses a 512GB boundary, ioremap() allocates a new pud table
and updates the kernel PGD entry to point it.  If user process's
PGD entry does not have this update yet, a read/write syscall
to the range will cause a vmalloc fault, which hits the Oops
above as it does not handle a large page properly.

Following changes are made to vmalloc_fault().


 - No change for the PGD sync operation as it handles large
   pages already.
 - Add pud_huge() and pmd_huge() to the validation code to
   handle large pages.
 - Change pud_page_vaddr() to pud_pfn() since an ioremap range
   is not directly mapped (while the if-statement still works
   with a bogus addr).
 - Change pmd_page() to pmd_pfn() since an ioremap range is not
   backed by struct page (while the if-statement still works
   with a bogus addr).

 - No change for the sync operation since the index3 PGD entry
   covers the entire vmalloc range, which is always valid.
   (A separate change to sync PGD entry is necessary if this
    memory layout is changed regardless of the page size.)
 - Add pmd_huge() to the validation code to handle large pages.
   This is for completeness since vmalloc_fault() won't happen
   in ioremap'd ranges as its PGD entry is always valid.

Reported-by: Henning Schild <henning.schild at siemens.com>
Signed-off-by: Toshi Kani <toshi.kani at hpe.com>
Acked-by: Borislav Petkov <bp at alien8.de>
Cc: <stable at vger.kernel.org> # 4.1+
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Brian Gerst <brgerst at gmail.com>
Cc: Denys Vlasenko <dvlasenk at redhat.com>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof at suse.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Toshi Kani <toshi.kani at hp.com>
Cc: linux-mm at kvack.org
Cc: linux-nvdimm at lists.01.org
Link: http://lkml.kernel.org/r/1455758214-24623-1-git-send-email-toshi.kani@hpe.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Henning Schild <henning.schild at siemens.com>
 arch/x86/mm/fault.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fd5bbcc..475106f 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -285,6 +285,9 @@ static noinline int vmalloc_fault(unsigned long address)
 	if (!pmd_k)
 		return -1;
+	if (pmd_huge(*pmd_k))
+		return 0;
 	pte_k = pte_offset_kernel(pmd_k, address);
 	if (!pte_present(*pte_k))
 		return -1;
@@ -356,8 +359,6 @@ void vmalloc_sync_all(void)
  * 64-bit:
  *   Handle a fault on the vmalloc area
- *
- * This assumes no large pages in there.
 static inline int vmalloc_sync_one(pgd_t *pgd, unsigned long address)
@@ -398,17 +399,23 @@ static inline int vmalloc_sync_one(pgd_t *pgd, unsigned long address)
 	if (pud_none(*pud_ref))
 		return -1;
-	if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
+	if (pud_none(*pud) || pud_pfn(*pud) != pud_pfn(*pud_ref))
+	if (pud_huge(*pud))
+		return 0;
 	pmd = pmd_offset(pud, address);
 	pmd_ref = pmd_offset(pud_ref, address);
 	if (pmd_none(*pmd_ref))
 		return -1;
-	if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
+	if (pmd_none(*pmd) || pmd_pfn(*pmd) != pmd_pfn(*pmd_ref))
+	if (pmd_huge(*pmd))
+		return 0;
 	pte_ref = pte_offset_kernel(pmd_ref, address);
 	if (!pte_present(*pte_ref))
 		return -1;

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