Re: [PATCH 0/1] Fix for riscv vmcore issue

[Alexandre Ghiti]

Hi Pnina,

On 7/3/25 14:06, Pnina Feder wrote:
> > Pnina!
> >
> > Pnina Feder <pnina.feder@xxxxxxxxxxxx> writes:
> >
> > > We are creating a vmcore using kexec on a Linux 6.15 RISC-V system and
> > > analyzing it with the crash tool on the host. This workflow used to
> > > work on Linux 6.14 but is now broken in 6.15.
> > Thanks for reporting this!
> >
> > > The issue is caused by a change in the kernel:
> > > In Linux 6.15, certain memblock sections are now marked as Reserved in
> > > /proc/iomem. The kexec tool excludes all Reserved regions when
> > > generating the vmcore, so these sections are missing from the dump.
> > How are you collecting the /proc/vmcore file? A full set of commands would be helpful.
> We’ve defined in our system that when a process crashes, we call panic().
> To handle crash recovery, we're using kexec with the following command:
> kexec -p /Image --initrd=/rootfs.cpio --append "console=${con} earlycon=${earlycon} no4lvl"
>
> To simulate crash, we trigger it using:
> sleep 100 & kill -6 $!
>
> This boots into the crash kernel (kdump), where we then copy the /proc/vmcore file back to the host for analysis.
>
> > > However, the kernel still uses addresses in these regions—for example,
> > > for IRQ pointers. Since the crash tool needs access to these memory
> > > areas to function correctly, their exclusion breaks the analysis.
> > Wdym with "IRQ pointers"? Also, what version (sha1) of crash are you using?
> We are currently using crash-utility version 9.0.0 (master).
>  From the crash analysis logs, we observed errors like:
>
> "......
> IRQ stack pointer[0] is  ffffffd6fbdcc068
> crash: read error: kernel virtual address: ffffffd6fbdcc068  type: "IRQ stack pointer"
> .....
>
> <read_kdump: addr: ffffffff80edf1cc paddr: 8010df1cc cnt: 4>
> <readmem: ffffffd6fbdd6880, KVADDR, "runqueues entry (per_cpu)", 3456, (FOE), 55acf03963e0>
> > read_kdump: addr: ffffffd6fbdd6880 paddr: 8fbdd6880 cnt: 1920<
> crash: read error: kernel virtual address: ffffffd6fbdd6880  type: "runqueues entry (per_cpu)"


I can't reproduce this issue on qemu, booting with sv39. I'm using the 
latest kexec-tools (which recently merged riscv support), crash 9.0.0 
and kernel 6.16.0-rc4. Note that I'm using crash in qemu.

Are you able to reproduce this on qemu too?

Maybe that's related to the config, can you share your config?


> These failures occur consistently for addresses in the 0xffffffd000000000 region.


FYI, this region is the direct mapping (see 
Documentation/arch/riscv/vm-layout.rst).

Thanks,

Alex


> Upon inspection, we confirmed that the physical addresses corresponding to those virtual addresses are not present in the vmcore, as they fall under Reserved memory sections.
> We tested a patch to kexec-tools that prevents exclusion of the Reserved-memblock section from the vmcore. With this patch, the issue no longer occurs, and crash analysis succeeds.
> Note: I suspect the same issue exists on ARM64, as both the signal.c and kexec-tools implementations are similar.
>
> > Thanks!
> > Björn