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Subject[PATCH] powerpc/mm: Comment arch_unmap()
Date
During a different patch review, the check in arch_munmap() was found
spucious due the lake of explanation.

Adding a comment to clarify the test.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
---
arch/powerpc/include/asm/mmu_context.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 6ee8195a2ffb..638f481b3c9f 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -240,6 +240,17 @@ static inline void arch_unmap(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
+ /*
+ * There are 2 assumptions here:
+ * 1. the VDSO is one page size (guaranteed by vdso_data_store)
+ * 2. 'start' and 'end' are page aligned (guaranteed by the caller)
+ * The test is wrote in a way to handle unmap operation surrounding the
+ * VDSO area like:
+ * | VDSO |
+ * ^ start ^ end
+ * The test also covers the munmap() operation done to the exact VDSO's
+ * boundaries.
+ */
if (start <= mm->context.vdso_base && mm->context.vdso_base < end)
mm->context.vdso_base = 0;
}
--
2.21.0
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