[PATCH 2/4] arm64: kdump: support reserving crashkernel above 4G

[Chen Zhou <chenzhou10@huawei.com>]

When crashkernel is reserved above 4G in memory, kernel should
reserve some amount of low memory for swiotlb and some DMA buffers.

Meanwhile, support crashkernel=X,[high,low] in arm64. When use
crashkernel=X parameter, try low memory first and fall back to high
memory unless "crashkernel=X,high" is specified.

Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
---
 arch/arm64/include/asm/kexec.h |  3 +++
 arch/arm64/kernel/setup.c      |  3 +++
 arch/arm64/mm/init.c           | 34 ++++++++++++++++++++++++++++------
 3 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
index 67e4cb7..32949bf 100644
--- a/arch/arm64/include/asm/kexec.h
+++ b/arch/arm64/include/asm/kexec.h
@@ -28,6 +28,9 @@
 
 #define KEXEC_ARCH KEXEC_ARCH_AARCH64
 
+/* 2M alignment for crash kernel regions */
+#define CRASH_ALIGN	SZ_2M
+
 #ifndef __ASSEMBLY__
 
 /**
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 413d566..82cd9a0 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -243,6 +243,9 @@ static void __init request_standard_resources(void)
 			request_resource(res, &kernel_data);
 #ifdef CONFIG_KEXEC_CORE
 		/* Userspace will find "Crash kernel" region in /proc/iomem. */
+		if (crashk_low_res.end && crashk_low_res.start >= res->start &&
+		    crashk_low_res.end <= res->end)
+			request_resource(res, &crashk_low_res);
 		if (crashk_res.end && crashk_res.start >= res->start &&
 		    crashk_res.end <= res->end)
 			request_resource(res, &crashk_res);
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index d2adffb..3fcd739 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -74,20 +74,37 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
 static void __init reserve_crashkernel(void)
 {
 	unsigned long long crash_base, crash_size;
+	bool high = false;
 	int ret;
 
 	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
 				&crash_size, &crash_base);
 	/* no crashkernel= or invalid value specified */
-	if (ret || !crash_size)
-		return;
+	if (ret || !crash_size) {
+		/* crashkernel=X,high */
+		ret = parse_crashkernel_high(boot_command_line,
+				memblock_phys_mem_size(),
+				&crash_size, &crash_base);
+		if (ret || !crash_size)
+			return;
+		high = true;
+	}
 
 	crash_size = PAGE_ALIGN(crash_size);
 
 	if (crash_base == 0) {
-		/* Current arm64 boot protocol requires 2MB alignment */
-		crash_base = memblock_find_in_range(0, ARCH_LOW_ADDRESS_LIMIT,
-				crash_size, SZ_2M);
+		/*
+		 * Try low memory first and fall back to high memory
+		 * unless "crashkernel=size[KMG],high" is specified.
+		 */
+		if (!high)
+			crash_base = memblock_find_in_range(0,
+					ARCH_LOW_ADDRESS_LIMIT,
+					crash_size, CRASH_ALIGN);
+		if (!crash_base)
+			crash_base = memblock_find_in_range(0,
+					memblock_end_of_DRAM(),
+					crash_size, CRASH_ALIGN);
 		if (crash_base == 0) {
 			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
 				crash_size);
@@ -105,13 +122,18 @@ static void __init reserve_crashkernel(void)
 			return;
 		}
 
-		if (!IS_ALIGNED(crash_base, SZ_2M)) {
+		if (!IS_ALIGNED(crash_base, CRASH_ALIGN)) {
 			pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n");
 			return;
 		}
 	}
 	memblock_reserve(crash_base, crash_size);
 
+	if (crash_base >= SZ_4G && reserve_crashkernel_low()) {
+		memblock_free(crash_base, crash_size);
+		return;
+	}
+
 	pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
 		crash_base, crash_base + crash_size, crash_size >> 20);
 
-- 
2.7.4