[PATCH v18 06/17] x86/setup: Update comments in reserve_crashkernel()

Zhen Lei
2021-12-22T13:12:33Z

Add comments to describe which bootup parameters are processed by the
code, and make comments close to the code being commented.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
arch/x86/kernel/setup.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 07a58313db5c5f7..52aa925877ca787 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -485,20 +485,20 @@ static void __init reserve_crashkernel(void)
if (flag == CRASHKERNEL_MEM_NONE)
return;

- /* 0 means: find the address automatically */
if (!crash_base) {
/*
- * Set CRASH_ADDR_LOW_MAX upper bound for crash memory,
- * crashkernel=x,high reserves memory over 4G, also allocates
- * 256M extra low memory for DMA buffers and swiotlb.
- * But the extra memory is not required for all machines.
- * So try low memory first and fall back to high memory
- * unless "crashkernel=size[KMG],high" is specified.
+ * For the case of crashkernel=X[@offset] and offset is omitted,
+ * try the low memory first.
*/
if (!(flag & CRASHKERNEL_MEM_HIGH))
crash_base = memblock_phys_alloc_range(crash_size,
CRASH_ALIGN, CRASH_ALIGN,
CRASH_ADDR_LOW_MAX);
+
+ /*
+ * If low memory allocation failed above, or for the case of
+ * crashkernel=X,high, try the high memory.
+ */
if (!crash_base)
crash_base = memblock_phys_alloc_range(crash_size,
CRASH_ALIGN, CRASH_ALIGN,
@@ -510,6 +510,10 @@ static void __init reserve_crashkernel(void)
} else {
unsigned long long start;

+ /*
+ * The case of crashkernel=X@offset and offset is specified.
+ * Only user-specified space can be reserved.
+ */
start = memblock_phys_alloc_range(crash_size, SZ_1M, crash_base,
crash_base + crash_size);
if (start != crash_base) {
@@ -520,6 +524,10 @@ static void __init reserve_crashkernel(void)

#ifdef CONFIG_X86_64
if (crash_base >= (1ULL << 32)) {
+ /*
+ * Ensure that at least 256M extra low memory is allocated for
+ * DMA buffers and swiotlb, if low memory size is not specified.
+ */
if (!(flag & CRASHKERNEL_MEM_LOW)) {
/*
* two parts from kernel/dma/swiotlb.c:
--
2.25.1