[PATCH v2 3/3] arm64: kdump: defer the crashkernel reservation for platforms with no DMA memory zones

[Baoquan He]

In commit 031495635b46 ("arm64: Do not defer reserve_crashkernel() for
platforms with no DMA memory zones"), reserve_crashkernel() is called
much earlier in arm64_memblock_init() to avoid causing base apge
mapping on platforms with no DMA meomry zones.

With taking off protection on crashkernel memory region, no need to call
reserve_crashkernel() specially in advance. The deferred invocation of
reserve_crashkernel() in bootmem_init() can cover all cases. So revert
the commit 031495635b46 now.

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
v1->v2:
- When trying to revert commit 031495635b46, two hunks were missed in v1
  post. Remove them in v2. Thanks to Leizhen for pointing out this. 
  - Remove code comment above arm64_dma_phys_limit definition added
    in commit 031495635b46;
  - Move the arm64_dma_phys_limit assignment back into zone_sizes_init()
    when both CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are not enabled.

 arch/arm64/include/asm/memory.h |  5 -----
 arch/arm64/mm/init.c            | 34 +++------------------------------
 2 files changed, 3 insertions(+), 36 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 78e5163836a0..efcd68154a3a 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -374,11 +374,6 @@ static inline void *phys_to_virt(phys_addr_t x)
 })
 
 void dump_mem_limit(void);
-
-static inline bool defer_reserve_crashkernel(void)
-{
-	return IS_ENABLED(CONFIG_ZONE_DMA) || IS_ENABLED(CONFIG_ZONE_DMA32);
-}
 #endif /* !ASSEMBLY */
 
 /*
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 58a0bb2c17f1..66e70ca47680 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -61,34 +61,8 @@ EXPORT_SYMBOL(memstart_addr);
  * unless restricted on specific platforms (e.g. 30-bit on Raspberry Pi 4).
  * In such case, ZONE_DMA32 covers the rest of the 32-bit addressable memory,
  * otherwise it is empty.
- *
- * Memory reservation for crash kernel either done early or deferred
- * depending on DMA memory zones configs (ZONE_DMA) --
- *
- * In absence of ZONE_DMA configs arm64_dma_phys_limit initialized
- * here instead of max_zone_phys().  This lets early reservation of
- * crash kernel memory which has a dependency on arm64_dma_phys_limit.
- * Reserving memory early for crash kernel allows linear creation of block
- * mappings (greater than page-granularity) for all the memory bank rangs.
- * In this scheme a comparatively quicker boot is observed.
- *
- * If ZONE_DMA configs are defined, crash kernel memory reservation
- * is delayed until DMA zone memory range size initialization performed in
- * zone_sizes_init().  The defer is necessary to steer clear of DMA zone
- * memory range to avoid overlap allocation.  So crash kernel memory boundaries
- * are not known when mapping all bank memory ranges, which otherwise means
- * not possible to exclude crash kernel range from creating block mappings
- * so page-granularity mappings are created for the entire memory range.
- * Hence a slightly slower boot is observed.
- *
- * Note: Page-granularity mappings are necessary for crash kernel memory
- * range for shrinking its size via /sys/kernel/kexec_crash_size interface.
  */
-#if IS_ENABLED(CONFIG_ZONE_DMA) || IS_ENABLED(CONFIG_ZONE_DMA32)
 phys_addr_t __ro_after_init arm64_dma_phys_limit;
-#else
-phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
-#endif
 
 /* Current arm64 boot protocol requires 2MB alignment */
 #define CRASH_ALIGN			SZ_2M
@@ -248,6 +222,8 @@ static void __init zone_sizes_init(void)
 	if (!arm64_dma_phys_limit)
 		arm64_dma_phys_limit = dma32_phys_limit;
 #endif
+	if (!arm64_dma_phys_limit)
+		arm64_dma_phys_limit = PHYS_MASK + 1;
 	max_zone_pfns[ZONE_NORMAL] = max_pfn;
 
 	free_area_init(max_zone_pfns);
@@ -408,9 +384,6 @@ void __init arm64_memblock_init(void)
 
 	early_init_fdt_scan_reserved_mem();
 
-	if (!defer_reserve_crashkernel())
-		reserve_crashkernel();
-
 	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
 }
 
@@ -457,8 +430,7 @@ void __init bootmem_init(void)
 	 * request_standard_resources() depends on crashkernel's memory being
 	 * reserved, so do it here.
 	 */
-	if (defer_reserve_crashkernel())
-		reserve_crashkernel();
+	reserve_crashkernel();
 
 	memblock_dump_all();
 }
-- 
2.34.1