Re: [Crash-utility] [PATCH] ppc64: do page traversal if vmemmap_list not populated
Hello lijiang,
On Mon, Sep 18, 2023 at 07:34:04PM +0800, lijiang wrote:
Hi, Aditya
Thank you for the patch.
On Mon, Sep 11, 2023 at 8:00 PM <crash-utility-request(a)redhat.com> wrote:
> ...
>
> Currently 'crash-tool' fails on vmcore collected on upstream kernel on
> PowerPC64 with the error:
>
> crash: invalid kernel virtual address: 0 type: "first list entry
>
> Presently the address translation for vmemmap addresses is done using
> the vmemmap_list. But with the below commit in Linux, vmemmap_list can
> be empty, in case of Radix MMU on PowerPC64
>
> 368a0590d954: (powerpc/book3s64/vmemmap: switch radix to use a
> different vmemmap handling function)
>
> In case vmemmap_list is empty, then it's head is NULL, which crash tries
> to access and fails due to accessing NULL.
>
> Instead of depending on 'vmemmap_list' for address translation for
> vmemmap addresses, do a kernel pagetable walk to get the physical
> address associated with given virtual address
>
> Reviewed-by: Hari Bathini <hbathini(a)linux.ibm.com>
> Signed-off-by: Aditya Gupta <adityag(a)linux.ibm.com>
>
> ---
>
> Testing
> =======
>
> Git tree with patch applied:
> https://github.com/adi-g15-ibm/crash/tree/bugzilla-203296-list-v1
>
> This can be tested with '/proc/vmcore' as the vmcore, since makedumpfile
>
Can you help to describe in detail how to reproduce this issue? Or does
this require any kernel configs to be enabled first? I did not reproduce
the current issue with '/proc/kcore' or vmcore(via cp).
Test kernel commit: ce9ecca0238b ("Linux 6.6-rc2")
# ./crash /home/linux/vmlinux
Thanks for testing it.
This issue occurs only in case of Radix MMU.
Overall, these are all the requirements:
1. Upstream linux (master branch) (your commit will also work, ce9ecca0238b)
2. 'CONFIG_PPC_BOOK3S_64' should be 'y' in kernel config (this should be
there
in default configs)
3. Check in dmesg of the crashed kernel, if it prints 'hash-mmu' or
'radix-mmu'. It should be 'radix-mmu'.
I guess, the system that was crashed might be using 'hash-mmu'.
also fails in absence of 'vmemmap_list' in upstream linux
Yes, it will fail in Hash MMU case, as we depend on 'vmemmap_list' in that case,
as the virtual to physical address mapping is not available in page table, in
case of Hash-MMU.
Only in radix MMU case, it will still work, even if 'vmemmap_list' is removed,
since we have the mappings in kernel page table, which is used by this patch.
Let me know if the issue still doesn't reproduce even after using a system with
Radix MMU.
Thanks,
- Aditya Gupta