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

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 26/07/26 16:26, 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 <sourabhjain@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. Have a single
> generic (non-rtas specific) function that accounts for high
> crashkernel support in different scenarios?

Yeah that's a good point. Having is_rtas_high_crashkernel_capable() for 
!CONFIG_PPC_RTAS
creates confusion. Single function to find high crashkernel support will 
be much better.

- Sourabh Jain

>
>>   #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;
>> +}
>> +
>>   void __init arch_reserve_crashkernel(void)
>>   {
>> -    unsigned long long crash_size, crash_base, crash_end;
>> +    unsigned long long crash_size, crash_base, crash_end, low_size = 0;
>>       unsigned long long kernel_start, kernel_size;
>>       unsigned long long total_mem_sz;
>> +    bool high = false;
>>       int ret;
>>         total_mem_sz = memory_limit ? memory_limit : 
>> memblock_phys_mem_size();
>>         /* use common parsing */
>>       ret = parse_crashkernel(boot_command_line, total_mem_sz, 
>> &crash_size,
>> -                &crash_base, NULL, &crashk_cma_size, NULL);
>> +                &crash_base, &low_size, &crashk_cma_size, &high);
>>         if (ret)
>>           return;
>>   -    crash_base = get_crash_base(crash_base);
>> -    crash_end = crash_base + crash_size - 1;
>> +    if (high && !high_crashkernel_supported()) {
>> +        high = false;
>> +        low_size = 0;
>> +        pr_warn("High crashkernel unsupported, using standard 
>> reservation");
>> +    }
>>   -    kernel_start = __pa(_stext);
>> -    kernel_size = _end - _stext;
>> +    if (high) {
>> +        crash_base = 0;
>> +    } else {
>> +        crash_base = get_crash_base(crash_base);
>> +        crash_end = crash_base + crash_size - 1;
>>   -    /* The crash region must not overlap the current kernel */
>> -    if ((kernel_start + kernel_size > crash_base) && (kernel_start 
>> <= crash_end)) {
>> -        pr_warn("Crash kernel can not overlap current kernel\n");
>> -        return;
>> +        kernel_start = __pa(_stext);
>> +        kernel_size = _end - _stext;
>> +
>> +        /* The crash region must not overlap the current kernel */
>> +        if ((kernel_start + kernel_size > crash_base) && 
>> (kernel_start <= crash_end)) {
>> +            pr_warn("Crash kernel can not overlap current kernel\n");
>> +            return;
>> +        }
>>       }
>>   -    reserve_crashkernel_generic(crash_size, crash_base, 0, false);
>> +    reserve_crashkernel_generic(crash_size, crash_base, low_size, 
>> high);
>>   }
>>     void __init kdump_cma_reserve(void)
>
> - Hari