[PATCH v4 02/14] arm: add support for folded p4d page tables

[Marek Szyprowski]

Hi

On 14.04.2020 17:34, Mike Rapoport wrote:
> From: Mike Rapoport <rppt at linux.ibm.com>
>
> Implement primitives necessary for the 4th level folding, add walks of p4d
> level where appropriate, and remove __ARCH_USE_5LEVEL_HACK.
>
> Signed-off-by: Mike Rapoport <rppt at linux.ibm.com>

Today I've noticed that kexec is broken on ARM 32bit. Bisecting between 
current linux-next and v5.7-rc1 pointed to this commit. I've tested this 
on Odroid XU4 and Raspberry Pi4 boards. Here is the relevant log:

# kexec --kexec-syscall -l zImage --append "$(cat /proc/cmdline)"
memory_range[0]:0x40000000..0xbe9fffff
memory_range[0]:0x40000000..0xbe9fffff
# kexec -e
kexec_core: Starting new kernel
8<--- cut here ---
Unable to handle kernel paging request at virtual address c010f1f4
pgd = c6817793
[c010f1f4] *pgd=4000041e(bad)
Internal error: Oops: 80d [#1] PREEMPT ARM
Modules linked in:
CPU: 0 PID: 1329 Comm: kexec Tainted: G        W 
5.7.0-rc3-00127-g6cba81ed0f62 #611
Hardware name: Samsung Exynos (Flattened Device Tree)
PC is at machine_kexec+0x40/0xfc
LR is at 0xffffffff
pc : [<c010f0b4>]    lr : [<ffffffff>]    psr: 60000013
sp : ebc13e60  ip : 40008000  fp : 00000001
r10: 00000058  r9 : fee1dead  r8 : 00000001
r7 : c121387c  r6 : 6c224000  r5 : ece40c00  r4 : ec222000
r3 : c010f1f4  r2 : c1100000  r1 : c1100000  r0 : 418d0000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 6bc14059  DAC: 00000051
Process kexec (pid: 1329, stack limit = 0x366bb4dc)
Stack: (0xebc13e60 to 0xebc14000)
...
[<c010f0b4>] (machine_kexec) from [<c01c0d84>] (kernel_kexec+0x74/0x7c)
[<c01c0d84>] (kernel_kexec) from [<c014b1bc>] (__do_sys_reboot+0x1f8/0x210)
[<c014b1bc>] (__do_sys_reboot) from [<c0100060>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xebc13fa8 to 0xebc13ff0)
...
---[ end trace 3e8d6c81723c778d ]---
1329 Segmentation fault      ./kexec -e

> ---
>   arch/arm/include/asm/pgtable.h     |  1 -
>   arch/arm/lib/uaccess_with_memcpy.c |  7 +++++-
>   arch/arm/mach-sa1100/assabet.c     |  2 +-
>   arch/arm/mm/dump.c                 | 29 +++++++++++++++++-----
>   arch/arm/mm/fault-armv.c           |  7 +++++-
>   arch/arm/mm/fault.c                | 22 ++++++++++------
>   arch/arm/mm/idmap.c                |  3 ++-
>   arch/arm/mm/init.c                 |  2 +-
>   arch/arm/mm/ioremap.c              | 12 ++++++---
>   arch/arm/mm/mm.h                   |  2 +-
>   arch/arm/mm/mmu.c                  | 35 +++++++++++++++++++++-----
>   arch/arm/mm/pgd.c                  | 40 ++++++++++++++++++++++++------
>   12 files changed, 125 insertions(+), 37 deletions(-)
>
> ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland