Re: Bug report: kernel paniced while booting
From: Alexandre Ghiti
Date: Tue Jun 06 2023 - 03:25:55 EST
On 06/06/2023 08:40, Sunil V L wrote:
On Mon, Jun 05, 2023 at 10:42:33PM +0100, Jessica Clarke wrote:
On 5 Jun 2023, at 16:12, Sunil V L <sunilvl@xxxxxxxxxxxxxxxx> wrote:
On Mon, Jun 05, 2023 at 04:25:06PM +0200, Alexandre Ghiti wrote:
Hi Song,
On Mon, Jun 5, 2023 at 12:52 PM Song Shuai <songshuaishuai@xxxxxxxxxxx> wrote:
Description of problem:
Booting Linux With RiscVVirtQemu edk2 firmware, a Store/AMO page fault was trapped to trigger a kernel panic.
The entire log has been posted at this link : https://termbin.com/nga4.
You can reproduce it with the following step :
1. prepare the environment with
- Qemu-virt: v8.0.0 (with OpenSbi v1.2)
- edk2 : at commit (2bc8545883 "UefiCpuPkg/CpuPageTableLib: Reduce the number of random tests")
- Linux : v6.4-rc1 and later version
2. start the Qemu virt board
```sh
$ cat ~/8_riscv/start_latest.sh
#!/bin/bash
/home/song/8_riscv/3_acpi/qemu/ooo/usr/local/bin/qemu-system-riscv64 \
-s -nographic -drive file=/home/song/8_riscv/3_acpi/Build_virt/RiscVVirtQemu/RELEASE_GCC5/FV/RISCV_VIRT.fd,if=pflash,format=raw,unit=1 \
-machine virt,acpi=off -smp 2 -m 2G \
-kernel /home/song/9_linux/linux/00_rv_def/arch/riscv/boot/Image \
-initrd /home/song/8_riscv/3_acpi/buildroot/output/images/rootfs.ext2 \
-append "root=/dev/ram ro console=ttyS0 earlycon=uart8250,mmio,0x10000000 efi=debug loglevel=8 memblock=debug" ## also panic by memtest
```
3. Then you will encounter the kernel panic logged in the above link
Other Information:
1. -------
This report is not identical to my prior report -- "kernel paniced when system hibernates" [1], but both of them
are closely related with the commit (3335068f8721 "riscv: Use PUD/P4D/PGD pages for the linear mapping").
With this commit, hibernation is trapped with "access fault" while accessing the PMP-protected regions (mmode_resv0@80000000)
from OpenSbi (BTW, hibernation is marked as nonportable by Conor[2]).
In this report, efi_init handoffs the memory mapping from Boot Services to memblock where reserves mmode_resv0@80000000,
so there is no "access fault" but "page fault".
And reverting commit 3335068f8721 indeed fixed this panic.
2. -------
As the gdb-pt-dump [3] tool shows, the PTE which covered the fault virtual address had the appropriate permission to store.
Is there another way to trigger the "Store/AMO page fault"? Or the creation of linear mapping in commit 3335068f8721 did something wrong?
```
(gdb) p/x $satp
$1 = 0xa000000000081708
(gdb) pt -satp 0xa000000000081708
Address : Length Permissions
0xff1bfffffea39000 : 0x1000 | W:1 X:0 R:1 S:1
0xff1bfffffebf9000 : 0x1000 | W:1 X:0 R:1 S:1
0xff1bfffffec00000 : 0x400000 | W:1 X:0 R:1 S:1
0xff60000000000000 : 0x1c0000 | W:1 X:0 R:1 S:1
0xff60000000200000 : 0xa00000 | W:0 X:0 R:1 S:1
0xff60000000c00000 : 0x7f000000 | W:1 X:0 R:1 S:1 // badaddr: ff6000007fdb1000
0xff6000007fdc0000 : 0x3d000 | W:1 X:0 R:1 S:1
0xff6000007ffbf000 : 0x1000 | W:1 X:0 R:1 S:1
0xffffffff80000000 : 0xc00000 | W:0 X:1 R:1 S:1
0xffffffff80c00000 : 0xa00000 | W:1 X:0 R:1 S:1
```
3. ------
You can also reproduce similar panic by appending "memtest" in kernel cmdline.
I have posted the memtest boot log at this link: https://termbin.com/1twl.
Please correct me if I'm wrong.
[1]: https://lore.kernel.org/linux-riscv/CAAYs2=gQvkhTeioMmqRDVGjdtNF_vhB+vm_1dHJxPNi75YDQ_Q@xxxxxxxxxxxxxx/
[2]: https://lore.kernel.org/linux-riscv/20230526-astride-detonator-9ae120051159@wendy/
[3]: https://github.com/martinradev/gdb-pt-dump
Thanks for the thorough report, really appreciated.
So there are multiple issues here:
- the first one is that the memory region for opensbi is marked as not
cacheable in the efi memory map, and then this region is not mapped in
the linear mapping:
[ 0.000000] efi: 0x000080000000-0x00008003ffff [Reserved | |
| | | | | | | | | | | |UC]
- the second one (that I feel a bit ashamed of...) is that I did not
check the alignment of the virtual address when choosing the map size
in best_map_size() and then we end up trying to map a physical region
aligned on 2MB that is actually not aligned on 2MB virtually because
the opensbi region is not mapped at all.
- the possible third one is that we should not map the linear mapping
using 4K pages, this would be slow in my opinion, and I think we
should waste a bit of memory to align va and pa on a 2MB boundary.
So I'll fix the second issue, and possibly the third one, and if no
one looks into why the opensbi region is mapped in UC, I'll take a
look at edk2.
Hi Alex,
EDK2 marks opensbi range as reserved memory in EFI map. According to DT
spec, if the no-map is not set, we need to mark it as
EfiBootServicesData but EfiBootServicesData is actually considered as
free memory in kernel, as per UEFI spec. To avoid kernel using this
memory, we deviated from the DT spec for opensbi ranges.
Violating specs is never the answer. Do one of:
1. Use no-map and take the performance hit
2. Exclude the memory range from /memory itself
3. Come up with a new no-access property that’s a weaker no-map
(i.e. that allows mapping and speculative access) and uses
EfiRuntimeServicesData in EFI land
2 feels most normal to me, personally, but all are fine.
Hi Jess,
IMO, all the physical memory installed by the user should be visible.
Some part of the memory may be reserved and not available for the user
but excluding from /memory can cause issues.
Whether we mark as EfiReservedMemory or EfiRuntimeServiceData, I think
it will be marked as no-map in memblock and can not be used by the OS
linear mapping. Alex can confirm this.
Yes, I think you're right, EfiRuntimeServiceData will be marked as
no-map anyway (see is_usable_memory()).
So, my preference is option 1.
Yes, again, I think you're right, this is feeling more and more like the
most "natural" solution to me too, we are struggling for a performance
benefit that was never proven...
Thanks,
Sunil
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