Re: [PATCH v2 4/4] powerpc/kdump: add support for high crashkernel reservation

[Sourabh Jain]

On 26/07/26 16:53, Hari Bathini wrote:

On 08/07/26 8:03 pm, Sourabh Jain wrote:

With this changes included crashkernel=xxM,high will be supported on
powerpc. This allow user to allocated crashkernel memory on higer memory
region and keeping the low memory allocation minimal.

The low memory reservation is by default set to 64 MB and it is reserved
below RTAS_INSTANTIATE_MAX (1G) to make sure rtas instantiation work
properly.

powerpc uses generic crashkernel parser and reserve functions and they
are capable of handling high crashkernel reservtion so
arch_reserve_crashkernel() is updated call generic crashkernel praser
and reserve function with resptive options to make
crashkernel=XXM,high prase and make crashkernel memory get reserved on
higher memory regions.

Note: High crashkernel is supported only on PPC 64-bit systems when
64-bit RTAS is instantiated and Radix MMU is enabled; otherwise, the
crashkernel reservation falls back to the default, even if the kernel
command includes crashkernel=XXM,high.

Signed-off-by: Sourabh Jain <sourabhj...@linux.ibm.com>
---
  arch/powerpc/include/asm/crash_reserve.h |  6 ++++
  arch/powerpc/include/asm/kexec.h         |  1 +
  arch/powerpc/include/asm/rtas.h          |  9 +++++
  arch/powerpc/kexec/core.c                | 45 +++++++++++++++++-------
  4 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/include/asm/crash_reserve.h b/arch/powerpc/include/asm/crash_reserve.h

index d1b570ddbf98..4f2096984736 100644
--- a/arch/powerpc/include/asm/crash_reserve.h
+++ b/arch/powerpc/include/asm/crash_reserve.h
@@ -2,6 +2,8 @@
  #ifndef _ASM_POWERPC_CRASH_RESERVE_H
  #define _ASM_POWERPC_CRASH_RESERVE_H
  +#include <asm/rtas.h>
+
  /* crash kernel regions are Page size agliged */
  #define CRASH_ALIGN             PAGE_SIZE
  @@ -12,5 +14,9 @@ static inline bool arch_add_crash_res_to_iomem(void)
  }
  #define arch_add_crash_res_to_iomem arch_add_crash_res_to_iomem
  #endif
+#define DEFAULT_CRASH_KERNEL_LOW_SIZE SZ_64M
+
+#define CRASH_ADDR_LOW_MAX    RTAS_INSTANTIATE_MAX
+#define CRASH_ADDR_HIGH_MAX    memblock_end_of_DRAM()
    #endif /* _ASM_POWERPC_CRASH_RESERVE_H */

diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h

index e02710d6a2e1..9e676bd3bf03 100644
--- a/arch/powerpc/include/asm/kexec.h
+++ b/arch/powerpc/include/asm/kexec.h

@@ -118,6 +118,7 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt, struct crash_mem   int __init overlaps_crashkernel(unsigned long start, unsigned long size);

  extern void arch_reserve_crashkernel(void);
  extern void kdump_cma_reserve(void);

+unsigned long long __init get_crash_base(unsigned long long crash_base);

  #else
  static inline void arch_reserve_crashkernel(void) {}

  static inline int overlaps_crashkernel(unsigned long start, unsigned long size) { return 0; } diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h

index aaa4c3bc1d61..d290437d8131 100644
--- a/arch/powerpc/include/asm/rtas.h
+++ b/arch/powerpc/include/asm/rtas.h

@@ -561,6 +561,14 @@ static inline int page_is_rtas_user_buf(unsigned long pfn)

      return 0;
  }
  +static inline bool is_rtas_high_crashkernel_capable(void)
+{
+    if (rtas_64)
+        return true;
+
+    return false;
+}
+

  /* Not the best place to put pSeries_coalesce_init, will be fixed when we

   * move some of the rtas suspend-me stuff to pseries */
  void pSeries_coalesce_init(void);
@@ -569,6 +577,7 @@ void rtas_initialize(void);

  static inline int page_is_rtas_user_buf(unsigned long pfn) { return 0;}

  static inline void pSeries_coalesce_init(void) { }
  static inline void rtas_initialize(void) { }

+static inline bool is_rtas_high_crashkernel_capable(void) { return true; }

Though !CONFIG_PPC_RTAS may imply radix MMU and high crashkernel
capable, is_rtas_high_crashkernel_capable() returning true for
!CONFIG_PPC_RTAS case seems counter-intuitive.

  #endif
    #ifdef CONFIG_HV_PERF_CTRS
diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
index dc44f11be353..81fc437377c8 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c
@@ -15,6 +15,7 @@
  #include <linux/irq.h>
  #include <linux/ftrace.h>
  +#include <asm/rtas.h>
  #include <asm/kdump.h>
  #include <asm/machdep.h>
  #include <asm/pgalloc.h>
@@ -64,7 +65,7 @@ void machine_kexec(struct kimage *image)
    static unsigned long long crashk_cma_size;

  -static unsigned long long __init get_crash_base(unsigned long long crash_base)

+unsigned long long __init get_crash_base(unsigned long long crash_base)
  {
    #ifndef CONFIG_NONSTATIC_KERNEL

@@ -104,35 +105,55 @@ static unsigned long long __init get_crash_base(unsigned long long crash_base)

  #endif
  }

+static bool high_crashkernel_supported(void)
+{

+#if defined(CONFIG_PPC64) && (defined(CONFIG_PPC_PSERIES) || defined(CONFIG_PPC_POWERNV))

+    if (early_radix_enabled() && is_rtas_high_crashkernel_capable())
+        return true;
+#endif
+    return false;
+}

Have this function that accounts for high crashkernel support in

different scenarios and drop is_rtas_high_crashkernel_capable()?

Agree.

- Sourabh Jain