linux-kernel - [PATCH] mm: HMM always needs MMU

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Date:   Fri, 25 Aug 2017 01:08:23 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Jérôme Glisse <jglisse@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Subhash Gutti <sgutti@...dia.com>,
        Evgeny Baskakov <ebaskakov@...dia.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: HMM always needs MMU_NOTIFIER

When building a kernel with HMM enabled but without MMU_NOTIFIER,
we run into a build error:

mm/hmm.c:66:22: error: field 'mmu_notifier' has incomplete type
  struct mmu_notifier mmu_notifier;

If I read this right, the dependency is correct, but the #ifdef
annotations in the mm/hmm.c are not. This changes them in
a way to make it all build cleanly.

Fixes: e4e0061ea15c ("mm/device-public-memory: device memory cache coherent with CPU")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
I did not try very hard to understand what the code is
supposed to do, please check if this makes sense beyond fixing
the build before applying.
---
 mm/hmm.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 4a179a16ab10..b9e9f14e7454 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -41,11 +41,16 @@
  */
 DEFINE_STATIC_KEY_FALSE(device_private_key);
 EXPORT_SYMBOL(device_private_key);
-static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
 
+void hmm_mm_destroy(struct mm_struct *mm)
+{
+	kfree(mm->hmm);
+}
+
+#if IS_ENABLED(CONFIG_HMM_MIRROR)
+static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
 
-#ifdef CONFIG_HMM
 /*
  * struct hmm - HMM per mm struct
  *
@@ -124,13 +129,6 @@ static struct hmm *hmm_register(struct mm_struct *mm)
 	return mm->hmm;
 }
 
-void hmm_mm_destroy(struct mm_struct *mm)
-{
-	kfree(mm->hmm);
-}
-#endif /* CONFIG_HMM */
-
-#if IS_ENABLED(CONFIG_HMM_MIRROR)
 static void hmm_invalidate_range(struct hmm *hmm,
 				 enum hmm_update_type action,
 				 unsigned long start,
-- 
2.9.0