[PATCH v5 2/5] kdump: implement reserve_crashkernel_cma

Jiri Bohac
2025-06-12T10:16:40Z

reserve_crashkernel_cma() reserves CMA ranges for the
crash kernel. If allocating the requested size fails,
try to reserve in smaller blocks.

Store the reserved ranges in the crashk_cma_ranges array
and the number of ranges in crashk_cma_cnt.

Signed-off-by: Jiri Bohac <jbohac@suse.cz>

---
Changes since v3:
- make reserve_crashkernel_cma() return early when cma_size == 0
to avoid printing out the 0 cma-allocated size

---
include/linux/crash_reserve.h | 12 ++++++++
kernel/crash_reserve.c | 52 +++++++++++++++++++++++++++++++++++
2 files changed, 64 insertions(+)

diff --git a/include/linux/crash_reserve.h b/include/linux/crash_reserve.h
index e784aaff2f5a..7b44b41d0a20 100644
--- a/include/linux/crash_reserve.h
+++ b/include/linux/crash_reserve.h
@@ -13,12 +13,24 @@
*/
extern struct resource crashk_res;
extern struct resource crashk_low_res;
+extern struct range crashk_cma_ranges[];
+#if defined(CONFIG_CMA) && defined(CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION)
+#define CRASHKERNEL_CMA
+#define CRASHKERNEL_CMA_RANGES_MAX 4
+extern int crashk_cma_cnt;
+#else
+#define crashk_cma_cnt 0
+#define CRASHKERNEL_CMA_RANGES_MAX 0
+#endif
+

int __init parse_crashkernel(char *cmdline, unsigned long long system_ram,
unsigned long long *crash_size, unsigned long long *crash_base,
unsigned long long *low_size, unsigned long long *cma_size,
bool *high);

+void __init reserve_crashkernel_cma(unsigned long long cma_size);
+
#ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
#ifndef DEFAULT_CRASH_KERNEL_LOW_SIZE
#define DEFAULT_CRASH_KERNEL_LOW_SIZE (128UL << 20)
diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
index a8861f3f64fe..ae32ea707678 100644
--- a/kernel/crash_reserve.c
+++ b/kernel/crash_reserve.c
@@ -14,6 +14,8 @@
#include <linux/cpuhotplug.h>
#include <linux/memblock.h>
#include <linux/kmemleak.h>
+#include <linux/cma.h>
+#include <linux/crash_reserve.h>

#include <asm/page.h>
#include <asm/sections.h>
@@ -469,6 +471,56 @@ void __init reserve_crashkernel_generic(unsigned long long crash_size,
#endif
}

+struct range crashk_cma_ranges[CRASHKERNEL_CMA_RANGES_MAX];
+#ifdef CRASHKERNEL_CMA
+int crashk_cma_cnt;
+void __init reserve_crashkernel_cma(unsigned long long cma_size)
+{
+ unsigned long long request_size = roundup(cma_size, PAGE_SIZE);
+ unsigned long long reserved_size = 0;
+
+ if (!cma_size)
+ return;
+
+ while (cma_size > reserved_size &&
+ crashk_cma_cnt < CRASHKERNEL_CMA_RANGES_MAX) {
+
+ struct cma *res;
+
+ if (cma_declare_contiguous(0, request_size, 0, 0, 0, false,
+ "crashkernel", &res)) {
+ /* reservation failed, try half-sized blocks */
+ if (request_size <= PAGE_SIZE)
+ break;
+
+ request_size = roundup(request_size / 2, PAGE_SIZE);
+ continue;
+ }
+
+ crashk_cma_ranges[crashk_cma_cnt].start = cma_get_base(res);
+ crashk_cma_ranges[crashk_cma_cnt].end =
+ crashk_cma_ranges[crashk_cma_cnt].start +
+ cma_get_size(res) - 1;
+ ++crashk_cma_cnt;
+ reserved_size += request_size;
+ }
+
+ if (cma_size > reserved_size)
+ pr_warn("crashkernel CMA reservation failed: %lld MB requested, %lld MB reserved in %d ranges\n",
+ cma_size >> 20, reserved_size >> 20, crashk_cma_cnt);
+ else
+ pr_info("crashkernel CMA reserved: %lld MB in %d ranges\n",
+ reserved_size >> 20, crashk_cma_cnt);
+}
+
+#else /* CRASHKERNEL_CMA */
+void __init reserve_crashkernel_cma(unsigned long long cma_size)
+{
+ if (cma_size)
+ pr_warn("crashkernel CMA reservation not supported\n");
+}
+#endif
+
#ifndef HAVE_ARCH_ADD_CRASH_RES_TO_IOMEM_EARLY
static __init int insert_crashkernel_resources(void)
{

--
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, Prague, Czechia