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

[Dave Young]

On 10/3/26 5:10 PM, Huacai Chen wrote:
> On Sat, Oct 3, 2026 at 4:25 PM Dave Young <yangrr.2009@xxxxxxxxxxxxxxx> wrote:
>>
>>
>>
>> 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.
> Hi, Dave. It is not completely a fixed value, and I found that RISC-V
> also exports PAGE_OFFSET.

The riscv part is more dynamic:
#define PAGE_OFFSET_L5          _AC(0xff60000000000000, UL)
#define PAGE_OFFSET_L4          _AC(0xffffaf8000000000, UL)
#define PAGE_OFFSET_L3          _AC(0xffffffd600000000, UL)
#define PAGE_OFFSET             kernel_map.page_offset

But for loongarch64, we need to calculate CACHE_BASE + PHYS_OFFSET, I assumed that CACHE_BASE is a fixed value ..


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