Re: [PATCH v2] LoongArch: kdump: add arch_crash_save_vmcoreinfo() support

[Dave Young]

On 9/28/26 10:28 PM, Huacai Chen wrote:
> Hi, Yangyang,
> 
> On Thu, Sep 24, 2026 at 3:58 PM Yangyang Lian <lianyangyang@xxxxxxxxxx> wrote:
>>
>> Since commit 23c85094fe18 ("proc/kcore: add vmcoreinfo note to
>> /proc/kcore") the kernel has exported the vmcoreinfo PT_NOTE on
>> /proc/kcore as wellas /proc/vmcore.
>>
>> LoongArch does not provide arch_crash_save_vmcoreinfo(), so the
>> arch-specific values are missing from the vmcoreinfo PT_NOTE. The
>> generic exporter in kernel/vmcore_info.c already provides
>> NUMBER(VMALLOC_START), but tools like crash cannot derive the module
>> and vmemmap ranges, VA_BITS, or the KASLR offset of a LoongArch dump.

current crash can get the kaslr offset from the _stext differ, so it just works, but maybe makedumpfile still need the vmcoreinfo export.

>>
>> Since commit 18210a104bb9 ("LoongArch: Expand module virtual address
>> space to 2GB") the vmalloc and module boundaries are no longer stable
>> across kernel versions either, so vmcoreinfo is the only reliable
>> source for them.
>>
>> Provide this function in a separate file that is built at the same time
>> as its caller in kernel/vmcore_info.c, and add a LOONGARCH64 section to
>> Documentation/admin-guide/kdump/vmcoreinfo.rst.
>>
>> Reported-by: Haoran Jiang <jianghaoran@xxxxxxxxxx>
>> Suggested-by: Haoran Jiang <jianghaoran@xxxxxxxxxx>
>> Tested-by: Tao Cui <cuitao@xxxxxxxxxx>
>> Co-developed-by: George Guo <guodongtai@xxxxxxxxxx>
>> Signed-off-by: George Guo <guodongtai@xxxxxxxxxx>
>> Signed-off-by: Yangyang Lian <lianyangyang@xxxxxxxxxx>
>> ---
>> V2 -> V1: Export VMEMMAP_END + 1 to make it an exclusive bound, matching
>>           what tools like makedumpfile expect.
>>           Add Tested-by tag from Tao Cui.
>>
>>  .../admin-guide/kdump/vmcoreinfo.rst          | 29 +++++++++++++++++++
>>  arch/loongarch/kernel/Makefile                |  1 +
>>  arch/loongarch/kernel/vmcore_info.c           | 21 ++++++++++++++
>>  3 files changed, 51 insertions(+)
>>  create mode 100644 arch/loongarch/kernel/vmcore_info.c
>>
>> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> index 7663c610fe90..2ff921232616 100644
>> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> @@ -594,3 +594,32 @@ va_kernel_pa_offset
>>
>>  Indicates the offset between the kernel virtual and physical mappings.
>>  Used to translate virtual to physical addresses.
>> +
>> +LOONGARCH64
>> +===========
>> +
>> +VA_BITS
>> +-------
>> +
>> +The maximum number of bits for virtual addresses. Used to compute the
>> +virtual memory ranges.
>> +
>> +PHYS_OFFSET
>> +-----------
>> +
>> +Indicates the physical address of the start of memory. Used to translate
>> +virtual to physical addresses.
>> +
>> +KERNELOFFSET
>> +------------
>> +
>> +The kernel randomization offset. Used to locate the kernel text in
>> +virtual memory. If KASLR is disabled, this value is zero.
>> +
>> +MODULES_VADDR|MODULES_END|VMALLOC_START|VMALLOC_END|VMEMMAP_START|VMEMMAP_END
>> +-----------------------------------------------------------------------------
>> +
>> +Used to get the correct ranges:
>> +       MODULES_VADDR ~ MODULES_END-1 : Kernel module space.
>> +       VMALLOC_START ~ VMALLOC_END-1 : vmalloc() / ioremap() space.
>> +       VMEMMAP_START ~ VMEMMAP_END-1 : vmemmap region, used for struct page array.
>> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
>> index 001924877772..6260c15adaba 100644
>> --- a/arch/loongarch/kernel/Makefile
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -64,6 +64,7 @@ obj-$(CONFIG_RELOCATABLE)     += relocate.o
>>  obj-$(CONFIG_KEXEC_CORE)       += machine_kexec.o relocate_kernel.o
>>  obj-$(CONFIG_KEXEC_FILE)       += machine_kexec_file.o kexec_efi.o kexec_elf.o
>>  obj-$(CONFIG_CRASH_DUMP)       += crash_dump.o
>> +obj-$(CONFIG_VMCORE_INFO)      += vmcore_info.o
>>
>>  obj-$(CONFIG_UNWINDER_GUESS)   += unwind_guess.o
>>  obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>> diff --git a/arch/loongarch/kernel/vmcore_info.c b/arch/loongarch/kernel/vmcore_info.c
>> new file mode 100644
>> index 000000000000..fb703b716253
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/vmcore_info.c
>> @@ -0,0 +1,21 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +#include <linux/vmcore_info.h>
>> +#include <asm/addrspace.h>
>> +#include <asm/pgtable.h>
>> +#include <asm/setup.h>
>> +
>> +void arch_crash_save_vmcoreinfo(void)
>> +{
>> +       VMCOREINFO_NUMBER(VA_BITS);
>> +       /* NUMBER(VMALLOC_START) is exported by the generic code */
>> +       vmcoreinfo_append_str("NUMBER(VMALLOC_END)=0x%lx\n", VMALLOC_END);
>> +#ifdef CONFIG_64BIT
>> +       vmcoreinfo_append_str("NUMBER(MODULES_VADDR)=0x%lx\n", MODULES_VADDR);
>> +       vmcoreinfo_append_str("NUMBER(MODULES_END)=0x%lx\n", MODULES_END);
>> +       vmcoreinfo_append_str("NUMBER(VMEMMAP_START)=0x%lx\n", (unsigned long)vmemmap);
>> +       vmcoreinfo_append_str("NUMBER(VMEMMAP_END)=0x%lx\n", VMEMMAP_END + 1);
>> +#endif
>> +       vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%lx\n", PHYS_OFFSET);
> I think it is also useful to export PAGE_OFFSET here.

Hi Huacai,  if it is a fixed value or it can be derived from other known values I'd suggest not to export.

> 
> Huacai
>> +       vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
>> +}
>> --
>> 2.25.1
>>
>>
> 
> 
>