linux-kernel - [PATCH v1 3/6] mm/memory_hotplug: restrict CONFIG_MEMORY

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Date:   Wed, 29 Sep 2021 16:35:57 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, Alex Shi <alexs@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Shuah Khan <shuah@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Rapoport <rppt@...nel.org>, x86@...nel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v1 3/6] mm/memory_hotplug: restrict CONFIG_MEMORY_HOTPLUG to 64 bit

32 bit support is broken in various ways: for example, we can online
memory that should actually go to ZONE_HIGHMEM to ZONE_MOVABLE or in
some cases even to one of the other kernel zones.

We marked it BROKEN in commit b59d02ed0869 ("mm/memory_hotplug: disable the
functionality for 32b") almost one year ago. According to that commit
it might be broken at least since 2017. Further, there is hardly a sane use
case nowadays.

Let's just depend completely on 64bit, dropping the "BROKEN" dependency to
make clear that we are not going to support it again. Next, we'll remove
some HIGHMEM leftovers from memory hotplug code to clean up.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index ea8762cd8e1e..88273dd5c6d6 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -125,7 +125,7 @@ config MEMORY_HOTPLUG
 	select MEMORY_ISOLATION
 	depends on SPARSEMEM
 	depends on ARCH_ENABLE_MEMORY_HOTPLUG
-	depends on 64BIT || BROKEN
+	depends on 64BIT
 	select NUMA_KEEP_MEMINFO if NUMA
 
 config MEMORY_HOTPLUG_DEFAULT_ONLINE
-- 
2.31.1