[PATCH RFC v1 1/3] powerpc/memtrace: Enforce power of 2 for memory buffer size

[David Hildenbrand <david@redhat.com>]

The code mentions "Trace memory needs to be aligned to the size", and
e.g., round_up() is documented to work on power of 2 only. Also, the
whole search is not optimized e.g., for being aligned to memory block
size only while allocating multiple memory blocks.

Let's just limit to powers of 2 that are at least the size of memory
blocks - the granularity we are using for alloc/offline/unplug.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Rashmica Gupta <rashmica.g@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 arch/powerpc/platforms/powernv/memtrace.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index eb2e75dac369..0c4c54d2e3c4 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -268,15 +268,11 @@ static int memtrace_online(void)
 
 static int memtrace_enable_set(void *data, u64 val)
 {
-	u64 bytes;
-
-	/*
-	 * Don't attempt to do anything if size isn't aligned to a memory
-	 * block or equal to zero.
-	 */
-	bytes = memory_block_size_bytes();
-	if (val & (bytes - 1)) {
-		pr_err("Value must be aligned with 0x%llx\n", bytes);
+	const unsigned long bytes = memory_block_size_bytes();
+
+	if (val && (!is_power_of_2(val) || val < bytes)) {
+		pr_err("Value must be 0 or a power of 2 (at least 0x%lx)\n",
+		       bytes);
 		return -EINVAL;
 	}
 
-- 
2.23.0