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

From: John Donnelly
Date: Mon Mar 21 2022 - 09:32:26 EST

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);