linux-kernel - [PATCH 4.6 098/203] arm64: mm: remove page_mapping check in __sync_icache

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Message-Id: <20160725203433.354128491@linuxfoundation.org>
Date:	Mon, 25 Jul 2016 13:55:13 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	Shaokun Zhang <zhangshaokun@...ilicon.com>
Subject: [PATCH 4.6 098/203] arm64: mm: remove page_mapping check in __sync_icache_dcache

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shaokun Zhang <zhangshaokun@...ilicon.com>

commit 20c27a4270c775d7ed661491af8ac03264d60fc6 upstream.

__sync_icache_dcache unconditionally skips the cache maintenance for
anonymous pages, under the assumption that flushing is only required in
the presence of D-side aliases [see 7249b79f6b4cc ("arm64: Do not flush
the D-cache for anonymous pages")].

Unfortunately, this breaks migration of anonymous pages holding
self-modifying code, where userspace cannot be reasonably expected to
reissue maintenance instructions in response to a migration.

This patch fixes the problem by removing the broken page_mapping(page)
check from the cache syncing code, otherwise we may end up fetching and
executing stale instructions from the PoU.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Mark Rutland <mark.rutland@....com>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Shaokun Zhang <zhangshaokun@...ilicon.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm64/mm/flush.c |    4 ----
 1 file changed, 4 deletions(-)

--- a/arch/arm64/mm/flush.c
+++ b/arch/arm64/mm/flush.c
@@ -71,10 +71,6 @@ void __sync_icache_dcache(pte_t pte, uns
 {
 	struct page *page = pte_page(pte);

-	/* no flushing needed for anonymous pages */
-	if (!page_mapping(page))
-		return;
-
 	if (!test_and_set_bit(PG_dcache_clean, &page->flags))
 		sync_icache_aliases(page_address(page),
 				    PAGE_SIZE << compound_order(page));