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From:   Geert Uytterhoeven <geert+renesas@glider.be>
To:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Geert Uytterhoeven <geert+renesas@glider.be>
Subject: [PATCH] memblock: Check memory add/cap ordering
Date:   Wed, 11 Aug 2021 10:55:18 +0200
Message-Id: <aabc5bad008d49f07d542815c6c8d28ec90bb09e.1628672091.git.geert+renesas@glider.be>
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For memblock_cap_memory_range() to work properly, it should be called
after memory is detected and added to memblock with memblock_add() or
memblock_add_node().  If memblock_cap_memory_range() would be called
before memory is registered, we may silently corrupt memory later
because the crash kernel will see all memory as available.

Print a warning and bail out if ordering is not satisfied.

Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 mm/memblock.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/memblock.c b/mm/memblock.c
index 57a9849a5d820c34..e2ca8ddc8ebebf4e 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1685,6 +1685,11 @@ void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
 	if (!size)
 		return;
 
+	if (memblock.memory.cnt <= 1) {
+		pr_warn("%s: No memory registered yet\n", __func__);
+		return;
+	}
+
 	ret = memblock_isolate_range(&memblock.memory, base, size,
 						&start_rgn, &end_rgn);
 	if (ret)
-- 
2.25.1