Bug report: kernel paniced when system hibernates

Song Shuai
2023-05-16T09:25:19Z

Description of problem:

The latest hibernation support[1] of RISC-V Linux produced a kernel panic.
The entire log has been posted at this link: https://termbin.com/sphl .

How reproducible:

You can reproduce it with the following step :

1. prepare the environment with
- Qemu-virt v8.0.0 (with OpenSbi v1.2)
- Linux v6.4-rc1

2. start the Qemu virt
```sh
$ cat ~/8_riscv/start_latest.sh
#!/bin/bash
/home/song/8_riscv/3_acpi/qemu/ooo/usr/local/bin/qemu-system-riscv64 \
-smp 2 -m 4G -nographic -machine virt \
-kernel /home/song/9_linux/linux/00_rv_test/arch/riscv/boot/Image \
-append "root=/dev/vda ro eaylycon=uart8250,mmio,0x10000000
early_ioremap_debug console=ttyS0 loglevel=8 memblock=debug
no_console_suspend audit=0 3" \
-drive file=/home/song/8_riscv/fedora/stage4-disk.img,format=raw,id=hd0 \
-device virtio-blk-device,drive=hd0 \
-drive file=/home/song/8_riscv/fedora/adisk.qcow2,format=qcow2,id=hd1 \
-device virtio-blk-device,drive=hd1 \
-gdb tcp::1236 #-S
```
3. execute hibernation

```sh
swapon /dev/vdb2 # this is my swap disk

echo disk > /sys/power/state
```

4. Then you will encounter the kernel panic logged in the above link

Other Information:

After my initial and incomplete dig-up, the commit (3335068f8721
"riscv: Use PUD/P4D/PGD pages for the linear mapping")[2]
is closely related to this panic. This commit uses re-defined
`MIN_MEMBLOCK_ADDR` to discover the entire system memory
and extends the `va_pa_offset` from `kernel_map.phys_addr` to
`phys_ram_base` for linear memory mapping.

If the firmware delivered the firmware memory region (like: a PMP
protected region in OpenSbi) without "no-map" propriety,
this commit will result in firmware memory being directly mapped by
`create_linear_mapping_page_table()`.

We can see the mapping via ptdump :
```c
---[ Linear mapping ]---
0xff60000000000000-0xff60000000200000 0x0000000080000000 2M PMD D A G
. . W R V ------------- the firmware memory
0xff60000000200000-0xff60000000c00000 0x0000000080200000 10M PMD D A G . . . R V
0xff60000000c00000-0xff60000001000000 0x0000000080c00000 4M PMD D A G . . W R V
0xff60000001000000-0xff60000001600000 0x0000000081000000 6M PMD D A G . . . R V
0xff60000001600000-0xff60000040000000 0x0000000081600000 1002M PMD D A
G . . W R V
0xff60000040000000-0xff60000100000000 0x00000000c0000000 3G PUD D A G . . W R V
---[ Modules/BPF mapping ]---
---[ Kernel mapping ]---
0xffffffff80000000-0xffffffff80a00000 0x0000000080200000 10M PMD D A G . X . R V
0xffffffff80a00000-0xffffffff80c00000 0x0000000080c00000 2M PMD D A G . . . R V
0xffffffff80c00000-0xffffffff80e00000 0x0000000080e00000 2M PMD D A G . . W R V
0xffffffff80e00000-0xffffffff81400000 0x0000000081000000 6M PMD D A G . . . R V
0xffffffff81400000-0xffffffff81800000 0x0000000081600000 4M PMD
```

In the hibernation process, `swsusp_save()` calls
`copy_data_pages(&copy_bm, &orig_bm)` to copy these two memory
bitmaps,
the Oops(load access fault) occurred while copying the page of
PAGE_OFFSET (which maps the firmware memory).

I also did two other tests:
Test1:

The hibernation works well in the kernel with the commit 3335068f8721
reverted at least in the current environment.

Test2:

I built a simple kernel module to simulate the access of the value of
`PAGE_OFFSET` address, and the same panic occurred with the load
access fault.
So hibernation seems not the only case to trigger this panic.

Finally, should we always leave the firmware memory with
`MEMBLOCK_NOMAP` flag by some efforts from Linux or OpenSbi (at least
in the current environment) or any other suggestions?

Please correct me if I'm wrong.

[1]: https://lore.kernel.org/r/20230330064321.1008373-5-jeeheng.sia@starfivetech.com
[2]: https://lore.kernel.org/r/20230324155421.271544-4-alexghiti@rivosinc.com

--
Thanks,
Song