Commit 8d306f53 authored Dec 04, 2017 by Heiko Carstens Committed by Martin Schwidefsky Dec 05, 2017

s390/mm: fix off-by-one bug in 5-level page table handling



Martin Cermak reported that setting a uprobe doesn't work. Reason for
this is that the common uprobes code tries to get an unmapped area at
the last possible page within an address space.

This broke with commit 1aea9b3f ("s390/mm: implement 5 level pages
tables") which introduced an off-by-one bug which prevents to map
anything at the last possible page within an address space.

The check with the off-by-one bug however can be removed since with
commit 8ab867cb ("s390/mm: fix BUG_ON in crst_table_upgrade") the
necessary check is done at both call sites.

Reported-by: Martin Cermak <mcermak@redhat.com>
Bisected-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Fixes: 1aea9b3f ("s390/mm: implement 5 level pages tables")
Cc: <stable@vger.kernel.org> # v4.13+
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 987b1549

arch/s390/mm/pgalloc.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -83,8 +83,6 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)

		/* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */
		VM_BUG_ON(mm->context.asce_limit < _REGION2_SIZE);
		if (end >= TASK_SIZE_MAX)
		return -ENOMEM;
		rc = 0;
		notify = 0;
		while (mm->context.asce_limit < end) {

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