[PATCH RFC 4.9 0/5] Fix booting arm64 big endian with QEMU 5.0.0+

[Greg Kroah-Hartman]

On Fri, Jan 07, 2022 at 12:43:30PM -0700, Nathan Chancellor wrote:
> Hello everyone,
> 
> After upgrading the version of QEMU used in our CI from 4.2.0 to 6.2.0,
> I noticed that our 4.9 arm64 big endian builds stopped booting properly.
> This is not something that is clang specific, I could reproduce it with
> GCC 8.3.0 (the rootfs is at [1]).
> 
> $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- distclean defconfig
> 
> $ scripts/config -e CPU_BIG_ENDIAN
> 
> $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- olddefconfig Image.gz
> 
> $ qemu-system-aarch64 \
>     -initrd rootfs.cpio \
>     -append 'console=ttyAMA0 earlycon' \
>     -cpu max \
>     -machine virt,gic-version=max \
>     -machine virtualization=true \
>     -display none \
>     -kernel arch/arm64/boot/Image.gz \
>     -m 512m \
>     -nodefaults \
>     -serial mon:stdio
> [    0.000000] Booting Linux on physical CPU 0x0
> [    0.000000] Linux version 4.9.296 (nathan at archlinux-ax161) (gcc version 8.3.0 (Debian 8.3.0-2) ) #1 SMP PREEMPT Fri Jan 7 19:10:49 UTC 2022
> ...
> [    0.773924] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> [    0.773924]
> [    0.776016] CPU: 0 PID: 1 Comm: init Not tainted 4.9.296 #1
> [    0.776149] Hardware name: linux,dummy-virt (DT)
> [    0.776375] Call trace:
> [    0.777063] [<ffff000008088ba0>] dump_backtrace+0x0/0x1b0
> [    0.777293] [<ffff000008088d64>] show_stack+0x14/0x20
> [    0.777420] [<ffff0000088c2d18>] dump_stack+0x98/0xb8
> [    0.777555] [<ffff0000088c0ee8>] panic+0x11c/0x278
> [    0.777684] [<ffff0000080c4d20>] do_exit+0x940/0x970
> [    0.777816] [<ffff0000080c4db8>] do_group_exit+0x38/0xa0
> [    0.777974] [<ffff0000080cf698>] get_signal+0xb8/0x678
> [    0.778111] [<ffff000008087ca8>] do_signal+0xd8/0x9b0
> [    0.778248] [<ffff0000080888dc>] do_notify_resume+0x8c/0xa8
> [    0.778392] [<ffff000008082ff4>] work_pending+0x8/0x10
> [    0.778790] Kernel Offset: disabled
> [    0.778891] Memory Limit: none
> [    0.779241] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> 
> I ended up bisecting QEMU down to cd3f80aba0 ("target/arm: Enable
> ARMv8.1-VHE in -cpu max") [2], which did not seem obviously broken. I
> noticed that our 4.14 builds were fine so I ended up doing a reverse
> bisect down to commit ec347012bbec ("arm64: sysreg: Move to use
> definitions for all the SCTLR bits"). Getting that change to apply
> cleanly involved applying the three other arm64 patches in this series
> and making it build properly required the BUILD_BUG_ON header split
> (including bug.h might have been sufficient but I did not want to risk
> any further breakage). I searched through mainline to see if there were
> any fixes commits that I missed and I did not find any.
> 
> I am not sure if this series would be acceptable in 4.9, hence the RFC
> tag. If not, I am happy to just spin down our boot tests of arm64 big
> endian on 4.9, which is not a super valuable target, but I figured I
> would send the series and let others decide!
> 
> [1]: https://github.com/ClangBuiltLinux/boot-utils/tree/6cfa15992d375dfb874ca0677abdaebfba4f74e6/images/arm64be
> [2]: https://gitlab.com/qemu-project/qemu/-/commit/cd3f80aba0c559a6291f7c3e686422b15381f6b7

Seems sane, having build coverage for 4.9 for the next year is always
good to keep going.  I'll queue these up now, thanks!

greg k-h