[PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace

[Will Deacon <will.deacon@arm.com>]

When allocating and returning clear huge pages to userspace as a
response to a fault, we may zero and return a mapping to a previously
dirtied physical region (for example, it may have been written by
a private mapping which was freed as a result of an ftruncate on the
backing file). On architectures with Harvard caches, this can lead to
I/D inconsistency since the zeroed view may not be visible to the
instruction stream.

This patch solves the problem by flushing the region after allocating
and clearing a new huge page. Note that PowerPC avoids this issue by
performing the flushing in their clear_user_page implementation to keep
the loader happy, however this is closely tied to the semantics of the
PG_arch_1 page flag which is architecture-specific.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 mm/hugetlb.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e198831..b83d026 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2646,6 +2646,7 @@ retry:
 			goto out;
 		}
 		clear_huge_page(page, address, pages_per_huge_page(h));
+		flush_dcache_page(page);
 		__SetPageUptodate(page);
 
 		if (vma->vm_flags & VM_MAYSHARE) {
-- 
1.7.4.1

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