Re: Bug report: kernel paniced while booting

[Atish Patra]

On Mon, Jun 5, 2023 at 8:13 AM 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]
> >

@Alex: The OpenSBI region is marked reserved because EDK2 chooses to
do that explicitly as explained by Sunil.
I don't think UC has to do anything with it. All the EFI memory regions are 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.
>

IMO, that should be the correct way unless we can change it to
EfiRunServicesData/Code.
Looking at U-Boot code, it sets the no-map region to
EfiBootServicesData which may cause
issues in RISC-V as well if we linear mapping sets up the initial 2MB.


> Let me know your thoughts how we can handle this better in EDK2
> considering it has to support ACPI also.
>
> Thanks,
> Sunil
>
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-- 
Regards,
Atish