Re: [PATCH -next v2 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

"chenjiahao (C)" <chenjiahao16@xxxxxxxxxx> · Thu, 30 Mar 2023 21:40:35 +0800

On 2023/3/29 19:19, Baoquan He wrote:
On 03/28/23 at 07:51pm, Chen Jiahao wrote:

Thanks for reviewing.

On riscv, the current crash kernel allocation logic is trying to
allocate within 32bit addressible memory region by default, if
failed, try to allocate without 4G restriction.

In need of saving DMA zone memory while allocating a relatively large
crash kernel region, allocating the reserved memory top down in
high memory, without overlapping the DMA zone, is a mature solution.
Here introduce the parameter option crashkernel=X,[high,low].

One can reserve the crash kernel from high memory above DMA zone range
by explicitly passing "crashkernel=X,high"; or reserve a memory range
below 4G with "crashkernel=X,low".

Signed-off-by: Chen Jiahao <chenjiahao16@xxxxxxxxxx>
---
  arch/riscv/kernel/setup.c |  5 ++++
  arch/riscv/mm/init.c      | 63 ++++++++++++++++++++++++++++++++++++---
  2 files changed, 64 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 5d3184cbf518..ea84e5047c23 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -176,6 +176,11 @@ static void __init init_resources(void)
  		if (ret < 0)
  			goto error;
  	}
+	if (crashk_low_res.start != crashk_low_res.end) {
+		ret = add_resource(&iomem_resource, &crashk_low_res);
+		if (ret < 0)
+			goto error;
+	}
  #endif
  
  #ifdef CONFIG_CRASH_DUMP
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 478d6763a01a..b7708cc467fa 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1152,6 +1152,28 @@ static inline void setup_vm_final(void)
  }
  #endif /* CONFIG_MMU */
  
+/* Reserve 128M low memory by default for swiotlb buffer */
+#define DEFAULT_CRASH_KERNEL_LOW_SIZE	(128UL << 20)
+
+static int __init reserve_crashkernel_low(unsigned long long low_size)
+{
+	unsigned long long low_base;
+
+	low_base = memblock_phys_alloc_range(low_size, PMD_SIZE, 0, dma32_phys_limit);
+	if (!low_base) {
+		pr_err("cannot allocate crashkernel low memory (size:0x%llx).\n", low_size);
+		return -ENOMEM;
+	}
+
+	pr_info("crashkernel low memory reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
+		low_base, low_base + low_size, low_size >> 20);
+
+	crashk_low_res.start = low_base;
+	crashk_low_res.end = low_base + low_size - 1;
+
+	return 0;
+}
+
  /*
   * reserve_crashkernel() - reserves memory for crash kernel
   *
@@ -1163,6 +1185,7 @@ static void __init reserve_crashkernel(void)
  {
  	unsigned long long crash_base = 0;
  	unsigned long long crash_size = 0;
+	unsigned long long crash_low_size = 0;
  	unsigned long search_start = memblock_start_of_DRAM();
  	unsigned long search_end = memblock_end_of_DRAM();
  
@@ -1182,8 +1205,30 @@ static void __init reserve_crashkernel(void)
  
  	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
  				&crash_size, &crash_base);
-	if (ret || !crash_size)
+	if (ret == -ENOENT) {
+		/*
+		 * crashkernel=X,[high,low] can be specified or not, but
+		 * invalid value is not allowed.
+		 */
+		ret = parse_crashkernel_high(boot_command_line, 0, &crash_size, &crash_base);
I would add a local variable to assign boot_command_line to it just like
arm64 does. Then these lines could be shorter.

	char *cmdline = boot_command_line;
Agreed, I will clean this up later in next version.
+		if (ret || !crash_size)
+			return;
+
+		/*
+		 * crashkernel=Y,low is valid only when crashkernel=X,high
+		 * is passed and high memory is reserved successful.
+		 */
+		ret = parse_crashkernel_low(boot_command_line, 0, &crash_low_size, &crash_base);
+		if (ret == -ENOENT)
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+		else if (ret)
+			return;
+
+		search_start = dma32_phys_limit;
+	} else if (ret || !crash_size) {
+		/* Invalid argument value specified */
  		return;
+	}
  
  	crash_size = PAGE_ALIGN(crash_size);
  
@@ -1201,16 +1246,26 @@ static void __init reserve_crashkernel(void)
  	 */
  	crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
  					       search_start,
-					       min(search_end, (unsigned long) SZ_4G));
+					       min(search_end, (unsigned long)dma32_phys_limit));
  	if (crash_base == 0) {
The above conditional check isn't right. If crashkernel=size@offset
specified, the reservation failure won't trigger retry. This seems to be
originally introduced by old commit, while this need be fixed firstly.

Just a little curious about the rule to cope with this specific case. If 
"crashkernel=size@offset" was passed

but reserve failed, should try again to allocate in high memory, 
regardless the specified size@offset,

or just throw a warning and return? Since I noticed the current logic 
here on Arm64 is to check if !fixed_base first

before retrying.


Or have I missed anything else?

-		/* Try again without restricting region to 32bit addressible memory */
+		/* Try again above the region of 32bit addressible memory */
  		crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
-						search_start, search_end);
+						       max(search_start, (unsigned long)dma32_phys_limit),
+						       search_end);
  		if (crash_base == 0) {
  			pr_warn("crashkernel: couldn't allocate %lldKB\n",
  				crash_size >> 10);
  			return;
  		}
+
+		if (!crash_low_size)
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+	}
+
+	if ((crash_base > dma32_phys_limit - crash_low_size) &&
+	    crash_low_size && reserve_crashkernel_low(crash_low_size)) {
+		memblock_phys_free(crash_base, crash_size);
+		return;
  	}
  
  	pr_info("crashkernel: reserved 0x%016llx - 0x%016llx (%lld MB)\n",
--
2.31.1

BR,

Jiahao







