From: Sourabh Jain <sourabhjain@linux.ibm.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>,
linuxppc-dev@lists.ozlabs.org
Cc: Baoquan he <bhe@redhat.com>, Jiri Bohac <jbohac@suse.cz>,
Hari Bathini <hbathini@linux.ibm.com>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Mahesh Salgaonkar <mahesh@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Shivang Upadhyay <shivangu@linux.ibm.com>,
kexec@lists.infradead.org
Subject: Re: [PATCH v5] powerpc/kdump: Add support for crashkernel CMA reservation
Date: Tue, 4 Nov 2025 10:48:51 +0530 [thread overview]
Message-ID: <7957bd55-5bda-406f-aab3-64e0620bd452@linux.ibm.com> (raw)
In-Reply-To: <87y0on4ebh.ritesh.list@gmail.com>
On 03/11/25 15:40, Ritesh Harjani (IBM) wrote:
> Sourabh Jain <sourabhjain@linux.ibm.com> writes:
>
>> Commit 35c18f2933c5 ("Add a new optional ",cma" suffix to the
>> crashkernel= command line option") and commit ab475510e042 ("kdump:
>> implement reserve_crashkernel_cma") added CMA support for kdump
>> crashkernel reservation.
>>
>> Extend crashkernel CMA reservation support to powerpc.
>>
>> The following changes are made to enable CMA reservation on powerpc:
>>
>> - Parse and obtain the CMA reservation size along with other crashkernel
>> parameters
>> - Call reserve_crashkernel_cma() to allocate the CMA region for kdump
>> - Include the CMA-reserved ranges in the usable memory ranges for the
>> kdump kernel to use.
>> - Exclude the CMA-reserved ranges from the crash kernel memory to
>> prevent them from being exported through /proc/vmcore.
>>
>> With the introduction of the CMA crashkernel regions,
>> crash_exclude_mem_range() needs to be called multiple times to exclude
>> both crashk_res and crashk_cma_ranges from the crash memory ranges. To
>> avoid repetitive logic for validating mem_ranges size and handling
>> reallocation when required, this functionality is moved to a new wrapper
>> function crash_exclude_mem_range_guarded().
>>
>> To ensure proper CMA reservation, reserve_crashkernel_cma() is called
>> after pageblock_order is initialized.
>>
>> Update kernel-parameters.txt to document CMA support for crashkernel on
>> powerpc architecture.
>>
>> Cc: Baoquan he <bhe@redhat.com>
>> Cc: Jiri Bohac <jbohac@suse.cz>
>> Cc: Hari Bathini <hbathini@linux.ibm.com>
>> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
>> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>> Cc: Shivang Upadhyay <shivangu@linux.ibm.com>
>> Cc: kexec@lists.infradead.org
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>> ---
>> Changlog:
>>
>> v3 -> v4
>> - Removed repeated initialization to tmem in
>> crash_exclude_mem_range_guarded()
>> - Call crash_exclude_mem_range() with right crashk ranges
>>
>> v4 -> v5:
>> - Document CMA-based crashkernel support for ppc64 in kernel-parameters.txt
>> ---
>> .../admin-guide/kernel-parameters.txt | 2 +-
>> arch/powerpc/include/asm/kexec.h | 2 +
>> arch/powerpc/kernel/setup-common.c | 4 +-
>> arch/powerpc/kexec/core.c | 10 ++++-
>> arch/powerpc/kexec/ranges.c | 43 ++++++++++++++-----
>> 5 files changed, 47 insertions(+), 14 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 6c42061ca20e..0f386b546cec 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1013,7 +1013,7 @@
>> It will be ignored when crashkernel=X,high is not used
>> or memory reserved is below 4G.
>> crashkernel=size[KMG],cma
>> - [KNL, X86] Reserve additional crash kernel memory from
>> + [KNL, X86, ppc64] Reserve additional crash kernel memory from
> Shouldn't this be PPC and not ppc64?
>
> If I see the crash_dump support...
>
> config ARCH_SUPPORTS_CRASH_DUMP
> def_bool PPC64 || PPC_BOOK3S_32 || PPC_85xx || (44x && !SMP)
>
> The changes below aren't specific to ppc64 correct?
The thing is this feature is only supported with KEXEC_FILE and which
only supported on PPC64:
config ARCH_SUPPORTS_KEXEC_FILE
def_bool PPC64
Hence I kept it as ppc64.
I think I should update that in the commit message.
Also do you think is it good to restrict this feature to KEXEC_FILE?
>
>> CMA. This reservation is usable by the first system's
>> userspace memory and kernel movable allocations (memory
>> balloon, zswap). Pages allocated from this memory range
>> diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h
>> index 4bbf9f699aaa..bd4a6c42a5f3 100644
>> --- a/arch/powerpc/include/asm/kexec.h
>> +++ b/arch/powerpc/include/asm/kexec.h
>> @@ -115,9 +115,11 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt, struct crash_mem
>> #ifdef CONFIG_CRASH_RESERVE
>> int __init overlaps_crashkernel(unsigned long start, unsigned long size);
>> extern void arch_reserve_crashkernel(void);
>> +extern void kdump_cma_reserve(void);
>> #else
>> static inline void arch_reserve_crashkernel(void) {}
>> static inline int overlaps_crashkernel(unsigned long start, unsigned long size) { return 0; }
>> +static inline void kdump_cma_reserve(void) { }
>> #endif
>>
>> #if defined(CONFIG_CRASH_DUMP)
>> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
>> index 68d47c53876c..c8c42b419742 100644
>> --- a/arch/powerpc/kernel/setup-common.c
>> +++ b/arch/powerpc/kernel/setup-common.c
>> @@ -35,6 +35,7 @@
>> #include <linux/of_irq.h>
>> #include <linux/hugetlb.h>
>> #include <linux/pgtable.h>
>> +#include <asm/kexec.h>
>> #include <asm/io.h>
>> #include <asm/paca.h>
>> #include <asm/processor.h>
>> @@ -995,11 +996,12 @@ void __init setup_arch(char **cmdline_p)
>> initmem_init();
>>
>> /*
>> - * Reserve large chunks of memory for use by CMA for fadump, KVM and
>> + * Reserve large chunks of memory for use by CMA for kdump, fadump, KVM and
>> * hugetlb. These must be called after initmem_init(), so that
>> * pageblock_order is initialised.
>> */
>> fadump_cma_init();
>> + kdump_cma_reserve();
>> kvm_cma_reserve();
>> gigantic_hugetlb_cma_reserve();
>>
>> diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
>> index d1a2d755381c..25744737eff5 100644
>> --- a/arch/powerpc/kexec/core.c
>> +++ b/arch/powerpc/kexec/core.c
>> @@ -33,6 +33,8 @@ void machine_kexec_cleanup(struct kimage *image)
>> {
>> }
>>
>> +unsigned long long cma_size;
>> +
> nit:
> Since this is a gloabal powerpc variable you are defining, then can we
> keep it's name to crashk_cma_size?
Yeah make sense. I will update the variable name.
>
>> /*
>> * Do not allocate memory (or fail in any way) in machine_kexec().
>> * We are past the point of no return, committed to rebooting now.
>> @@ -110,7 +112,7 @@ void __init arch_reserve_crashkernel(void)
>>
>> /* use common parsing */
>> ret = parse_crashkernel(boot_command_line, total_mem_sz, &crash_size,
>> - &crash_base, NULL, NULL, NULL);
>> + &crash_base, NULL, &cma_size, NULL);
>>
>> if (ret)
>> return;
>> @@ -130,6 +132,12 @@ void __init arch_reserve_crashkernel(void)
>> reserve_crashkernel_generic(crash_size, crash_base, 0, false);
>> }
>>
>> +void __init kdump_cma_reserve(void)
>> +{
>> + if (cma_size)
>> + reserve_crashkernel_cma(cma_size);
>> +}
>> +
> nit:
> cma_size is already checked for null within reserve_crashkernel_cma(),
> so we don't really need kdump_cma_reserve() function call as such.
>
> Also kdump_cma_reserve() only make sense with #ifdef CRASHKERNEL_CMA..
> so instead do you think we can directly call reserve_crashkernel_cma(cma_size)?
I think the above kdump_cma_reserve() definition should come under
CONFIG_CRASH_RESERVE
because the way it is declared in arch/powerpc/include/asm/kexec.h.
I would like to keep kdump_cma_reserve() as is it because of two reasons:
- It keeps setup_arch() free from kdump #ifdefs
- In case if we want to add some condition on this reservation it would
straight forward.
So lets keep kdump_cma_reserve as is, unless you have strong opinion on
not to.
>> int __init overlaps_crashkernel(unsigned long start, unsigned long size)
>> {
>> return (start + size) > crashk_res.start && start <= crashk_res.end;
>> diff --git a/arch/powerpc/kexec/ranges.c b/arch/powerpc/kexec/ranges.c
>> index 3702b0bdab14..3bd27c38726b 100644
>> --- a/arch/powerpc/kexec/ranges.c
>> +++ b/arch/powerpc/kexec/ranges.c
>> @@ -515,7 +515,7 @@ int get_exclude_memory_ranges(struct crash_mem **mem_ranges)
>> */
>> int get_usable_memory_ranges(struct crash_mem **mem_ranges)
>> {
>> - int ret;
>> + int ret, i;
>>
>> /*
>> * Early boot failure observed on guests when low memory (first memory
>> @@ -528,6 +528,13 @@ int get_usable_memory_ranges(struct crash_mem **mem_ranges)
>> if (ret)
>> goto out;
>>
>> + for (i = 0; i < crashk_cma_cnt; i++) {
>> + ret = add_mem_range(mem_ranges, crashk_cma_ranges[i].start,
>> + crashk_cma_ranges[i].end - crashk_cma_ranges[i].start + 1);
>> + if (ret)
>> + goto out;
>> + }
>> +
>> ret = add_rtas_mem_range(mem_ranges);
>> if (ret)
>> goto out;
>> @@ -546,6 +553,22 @@ int get_usable_memory_ranges(struct crash_mem **mem_ranges)
>> #endif /* CONFIG_KEXEC_FILE */
>>
>> #ifdef CONFIG_CRASH_DUMP
>> +static int crash_exclude_mem_range_guarded(struct crash_mem **mem_ranges,
>> + unsigned long long mstart,
>> + unsigned long long mend)
>> +{
>> + struct crash_mem *tmem = *mem_ranges;
>> +
>> + /* Reallocate memory ranges if there is no space to split ranges */
>> + if (tmem && (tmem->nr_ranges == tmem->max_nr_ranges)) {
>> + tmem = realloc_mem_ranges(mem_ranges);
>> + if (!tmem)
>> + return -ENOMEM;
>> + }
>> +
>> + return crash_exclude_mem_range(tmem, mstart, mend);
>> +}
>> +
>> /**
>> * get_crash_memory_ranges - Get crash memory ranges. This list includes
>> * first/crashing kernel's memory regions that
>> @@ -557,7 +580,6 @@ int get_usable_memory_ranges(struct crash_mem **mem_ranges)
>> int get_crash_memory_ranges(struct crash_mem **mem_ranges)
>> {
>> phys_addr_t base, end;
>> - struct crash_mem *tmem;
>> u64 i;
>> int ret;
>>
>> @@ -582,19 +604,18 @@ int get_crash_memory_ranges(struct crash_mem **mem_ranges)
>> sort_memory_ranges(*mem_ranges, true);
>> }
>>
>> - /* Reallocate memory ranges if there is no space to split ranges */
>> - tmem = *mem_ranges;
>> - if (tmem && (tmem->nr_ranges == tmem->max_nr_ranges)) {
>> - tmem = realloc_mem_ranges(mem_ranges);
>> - if (!tmem)
>> - goto out;
>> - }
>> -
>> /* Exclude crashkernel region */
>> - ret = crash_exclude_mem_range(tmem, crashk_res.start, crashk_res.end);
>> + ret = crash_exclude_mem_range_guarded(mem_ranges, crashk_res.start, crashk_res.end);
>> if (ret)
>> goto out;
>>
>> + for (i = 0; i < crashk_cma_cnt; ++i) {
>> + ret = crash_exclude_mem_range_guarded(mem_ranges, crashk_cma_ranges[i].start,
>> + crashk_cma_ranges[i].end);
>> + if (ret)
>> + goto out;
>> + }
>> +
>> /*
>> * FIXME: For now, stay in parity with kexec-tools but if RTAS/OPAL
>> * regions are exported to save their context at the time of
>> --
>> 2.51.0
next prev parent reply other threads:[~2025-11-04 5:19 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-03 4:37 [PATCH v5] powerpc/kdump: Add support for crashkernel CMA reservation Sourabh Jain
2025-11-03 10:10 ` Ritesh Harjani
2025-11-04 5:18 ` Sourabh Jain [this message]
2025-11-04 9:34 ` Sourabh Jain
2025-11-04 10:24 ` Ritesh Harjani
2025-11-04 12:38 ` Sourabh Jain
2025-11-04 10:18 ` Ritesh Harjani
2025-11-04 10:35 ` Sourabh Jain
2025-11-04 10:51 ` Ritesh Harjani
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