[PATCH 1/2] memblock tests: model the low allocation limit within dummy memory

[Tianyi Chen <hi@tychen.cc>]

The simulator represents physical addresses using the address of its
allocated buffer. That buffer can lie above the default
ARCH_LOW_ADDRESS_LIMIT, preventing meaningful memblock_alloc_low()
tests.

Use the existing architecture override in asm/dma.h to place the limit
halfway through the dummy memory buffer. Resolve it after the buffer
has been allocated, so both low and high memory can be represented
regardless of its address. The production allocator is unchanged.

Assisted-by: LLM
Signed-off-by: Tianyi Chen <hi@tychen.cc>
---
 tools/testing/memblock/asm/dma.h      | 6 ++++++
 tools/testing/memblock/tests/common.c | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/tools/testing/memblock/asm/dma.h b/tools/testing/memblock/asm/dma.h
index 13ff8e5d22e..6607408dcf2 100644
--- a/tools/testing/memblock/asm/dma.h
+++ b/tools/testing/memblock/asm/dma.h
@@ -2,4 +2,10 @@
 #ifndef _TOOLS_DMA_H
 #define _TOOLS_DMA_H
 
+#include <linux/types.h>
+
+phys_addr_t dummy_physical_memory_low_limit(void);
+
+#define ARCH_LOW_ADDRESS_LIMIT dummy_physical_memory_low_limit()
+
 #endif
diff --git a/tools/testing/memblock/tests/common.c b/tools/testing/memblock/tests/common.c
index 3250c8e5124..4e6a920c459 100644
--- a/tools/testing/memblock/tests/common.c
+++ b/tools/testing/memblock/tests/common.c
@@ -118,6 +118,11 @@ phys_addr_t dummy_physical_memory_base(void)
 	return (phys_addr_t)memory_block.base;
 }
 
+phys_addr_t dummy_physical_memory_low_limit(void)
+{
+	return dummy_physical_memory_base() + MEM_SIZE / 2;
+}
+
 static void usage(const char *prog)
 {
 	BUILD_BUG_ON(ARRAY_SIZE(help_opts) != ARRAY_SIZE(long_opts) - 1);
-- 
2.55.0