[PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

Zhen Lei
2022-07-11T09:04:59Z

To be consistent with the implementation of x86 and improve cross-platform
user experience. Try to allocate at least 256 MiB low memory automatically
for the case that crashkernel=,high is explicitly specified, while
crashkenrel=,low is omitted.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
Documentation/admin-guide/kernel-parameters.txt | 8 +-------
arch/arm64/mm/init.c | 12 +++++++++++-
2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2522b11e593f239..65a2c3a22a4b57d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -843,7 +843,7 @@
available.
It will be ignored if crashkernel=X is specified.
crashkernel=size[KMG],low
- [KNL, X86-64] range under 4G. When crashkernel=X,high
+ [KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
is passed, kernel could allocate physical memory region
above 4G, that cause second kernel crash on system
that require some amount of low memory, e.g. swiotlb
@@ -857,12 +857,6 @@
It will be ignored when crashkernel=X,high is not used
or memory reserved is below 4G.

- [KNL, ARM64] range in low memory.
- This one lets the user specify a low range in the
- DMA zone for the crash dump kernel.
- It will be ignored when crashkernel=X,high is not used
- or memory reserved is located in the DMA zones.
-
cryptomgr.notests
[KNL] Disable crypto self-tests

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 339ee84e5a61a0b..5390f361208ccf7 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
#define CRASH_ADDR_LOW_MAX arm64_dma_phys_limit
#define CRASH_ADDR_HIGH_MAX (PHYS_MASK + 1)

+/*
+ * 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;
@@ -147,7 +155,9 @@ static void __init reserve_crashkernel(void)
* is not allowed.
*/
ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
- if (ret && (ret != -ENOENT))
+ if (ret == -ENOENT)
+ crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+ else if (ret)
return;

crash_max = CRASH_ADDR_HIGH_MAX;
--
2.25.1