x86/mpx: Do not count MPX VMAs as neighbors when unmapping (bea03c50) · Commits · 戴 / test

The comment pretty much says it all. I wrote a test program that does lots of random allocations and forces bounds tables to be created. It came up with a layout like this: .... | BOUNDS DIRECTORY ENTRY COVERS | .... | BOUNDS TABLE COVERS | | BOUNDS TABLE | REAL ALLOC | BOUNDS TABLE | Unmapping "REAL ALLOC" should have been able to free the bounds table "covering" the "REAL ALLOC" because it was the last real user. But, the neighboring VMA bounds tables were found, considered as real neighbors, and we declined to free the bounds table covering the area. Doing this over and over left a small but significant number of these orphans. Handling them is fairly straighforward. All we have to do is walk the VMAs and skip all of the MPX ones when looking for neighbors. Signed-off-by:

Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by:

Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Hansen <dave@sr71.net> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20150607183706.A6BD90BF@viggo.jf.intel.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/mm/mpx.c

+19 −5

Original line number	Diff line number	Diff line
		@@ -936,17 +936,31 @@ static int try_unmap_single_bt(struct mm_struct *mm,
		unsigned long uninitialized_var(bt_addr);
		void __user *bde_vaddr;
		int ret;
		/*
		* We already unlinked the VMAs from the mm's rbtree so 'start'
		* is guaranteed to be in a hole. This gets us the first VMA
		* before the hole in to 'prev' and the next VMA after the hole
		* in to 'next'.
		*/
		next = find_vma_prev(mm, start, &prev);
		/*
		* Do not count other MPX bounds table VMAs as neighbors.
		* Although theoretically possible, we do not allow bounds
		* tables for bounds tables so our heads do not explode.
		* If we count them as neighbors here, we may end up with
		* lots of tables even though we have no actual table
		* entries in use.
		*/
		while (next && is_mpx_vma(next))
		next = next->vm_next;
		while (prev && is_mpx_vma(prev))
		prev = prev->vm_prev;
		/*
		* We know 'start' and 'end' lie within an area controlled
		* by a single bounds table. See if there are any other
		* VMAs controlled by that bounds table. If there are not
		* then we can "expand" the are we are unmapping to possibly
		* cover the entire table.
		*
		* We already unliked the VMAs from the mm's rbtree so 'start'
		* is guaranteed to be in a hole. This gets us the first VMA
		* before the hole in to 'prev' and the next VMA after the hole
		* in to 'next'.
		*/
		next = find_vma_prev(mm, start, &prev);
		if ((!prev \|\| prev->vm_end <= bta_start_vaddr) &&

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