Re: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X

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On 2/26/22 9:07 PM, Zhen Lei wrote:
From: Chen Zhou <chenzhou10@xxxxxxxxxx>

There are following issues in arm64 kdump:
1. We use crashkernel=X to reserve crashkernel below 4G, which
will fail when there is no enough low memory.

                        " Not enough "
2. If reserving crashkernel above 4G, in this case, crash dump
kernel will boot failure because there is no low memory available
for allocation.

 We can't have a "boot failure". If the requested reservation
 can not be met,  the kdump  configuration is not setup.

To solve these issues, change the behavior of crashkernel=X and
introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
in DMA zone, and fall back to high allocation if it fails.
We can also use "crashkernel=X,high" to select a region above DMA zone,
which also tries to allocate at least 256M in DMA zone automatically.
"crashkernel=Y,low" can be used to allocate specified size low memory.

Is there going to be documentation on what values certain Arm platforms are going to use this on ?


Signed-off-by: Chen Zhou <chenzhou10@xxxxxxxxxx>
Co-developed-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
  arch/arm64/kernel/machine_kexec.c      |   9 ++-
  arch/arm64/kernel/machine_kexec_file.c |  12 ++-
  arch/arm64/mm/init.c                   | 106 +++++++++++++++++++++++--
  3 files changed, 115 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index e16b248699d5c3c..19c2d487cb08feb 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -329,8 +329,13 @@ bool crash_is_nosave(unsigned long pfn)
/* in reserved memory? */
  	addr = __pfn_to_phys(pfn);
-	if ((addr < crashk_res.start) || (crashk_res.end < addr))
-		return false;
+	if ((addr < crashk_res.start) || (crashk_res.end < addr)) {
+		if (!crashk_low_res.end)
+			return false;
+
+		if ((addr < crashk_low_res.start) || (crashk_low_res.end < addr))
+			return false;
+	}
if (!kexec_crash_image)
  		return true;
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index 59c648d51848886..889951291cc0f9c 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -65,10 +65,18 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
/* Exclude crashkernel region */
  	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
+	if (ret)
+		goto out;
+
+	if (crashk_low_res.end) {
+		ret = crash_exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
+		if (ret)
+			goto out;
+	}
- if (!ret)
-		ret =  crash_prepare_elf64_headers(cmem, true, addr, sz);
+	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+out:
  	kfree(cmem);
  	return ret;
  }
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 90f276d46b93bc6..30ae6638ff54c47 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -65,6 +65,44 @@ EXPORT_SYMBOL(memstart_addr);
  phys_addr_t arm64_dma_phys_limit __ro_after_init;
#ifdef CONFIG_KEXEC_CORE
+/* Current arm64 boot protocol requires 2MB alignment */
+#define CRASH_ALIGN			SZ_2M
+
+#define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
+#define CRASH_ADDR_HIGH_MAX		memblock.current_limit
+
+/*
+ * This is an empirical value in x86_64 and taken here directly. Please
+ * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
+ * details.
+ */
+#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
+	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
+
+static int __init reserve_crashkernel_low(unsigned long long low_size)
+{
+	unsigned long long low_base;
+
+	/* passed with crashkernel=0,low ? */
+	if (!low_size)
+		return 0;
+
+	low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
+	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%08llx - 0x%08llx (%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;
+	insert_resource(&iomem_resource, &crashk_low_res);
+
+	return 0;
+}
+
  /*
   * reserve_crashkernel() - reserves memory for crash kernel
   *
@@ -75,30 +113,79 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
  static void __init reserve_crashkernel(void)
  {
  	unsigned long long crash_base, crash_size;
-	unsigned long long crash_max = arm64_dma_phys_limit;
+	unsigned long long crash_low_size;
+	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
  	int ret;
+	bool fixed_base, high = false;
+	char *cmdline = boot_command_line;
- ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
+	/* crashkernel=X[@offset] */
+	ret = parse_crashkernel(cmdline, 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(cmdline, 0, &crash_size, &crash_base);
+		if (ret || !crash_size)
+			return;
+
+		/* crashkernel=Y,low */
+		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
+		if (ret == -ENOENT)
+			/*
+			 * crashkernel=Y,low is not specified explicitly, use
+			 * default size automatically.
+			 */
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+		else if (ret)
+			/* crashkernel=Y,low is specified but Y is invalid */
+			return;
+
+		/* Mark crashkernel=X,high is specified */
+		high = true;
+		crash_max = CRASH_ADDR_HIGH_MAX;
+	}
+ fixed_base = !!crash_base;
  	crash_size = PAGE_ALIGN(crash_size);
/* User specifies base address explicitly. */
-	if (crash_base)
+	if (fixed_base)
  		crash_max = crash_base + crash_size;
- /* Current arm64 boot protocol requires 2MB alignment */
-	crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
+retry:
+	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
  					       crash_base, crash_max);
  	if (!crash_base) {
+		/*
+		 * Attempt to fully allocate low memory failed, fall back
+		 * to high memory, the minimum required low memory will be
+		 * reserved later.
+		 */
+		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
+			crash_max = CRASH_ADDR_HIGH_MAX;
+			goto retry;
+		}
+
  		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
  			crash_size);
  		return;
  	}
+ if (crash_base >= SZ_4G) {
+		/*
+		 * For case crashkernel=X, low memory is not enough and fall
+		 * back to reserve specified size of memory above 4G, try to
+		 * allocate minimum required memory below 4G again.
+		 */
+		if (!high)
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+
+		if (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",
  		crash_base, crash_base + crash_size, crash_size >> 20);
@@ -107,6 +194,9 @@ static void __init reserve_crashkernel(void)
  	 * map. Inform kmemleak so that it won't try to access it.
  	 */
  	kmemleak_ignore_phys(crash_base);
+	if (crashk_low_res.end)
+		kmemleak_ignore_phys(crashk_low_res.start);
+
  	crashk_res.start = crash_base;
  	crashk_res.end = crash_base + crash_size - 1;
  	insert_resource(&iomem_resource, &crashk_res);


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