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

[Marek Szyprowski]

Hi Mike,

On 08.05.2020 19:42, Mike Rapoport wrote:
> On Fri, May 08, 2020 at 08:53:27AM +0200, Marek Szyprowski wrote:
>> On 07.05.2020 18:11, Mike Rapoport wrote:
>>> On Thu, May 07, 2020 at 02:16:56PM +0200, Marek Szyprowski wrote:
>>>> On 14.04.2020 17:34, Mike Rapoport wrote:
>>>>> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>>>>>
>>>>> 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@xxxxxxxxxxxxx>
>>>> 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: GÂÂÂÂÂÂÂ W
>>>> 5.7.0-rc3-00127-g6cba81ed0f62 #611
>>>> Hardware name: Samsung Exynos (Flattened Device Tree)
>>>> PC is at machine_kexec+0x40/0xfc
>>> Any chance you have the debug info in this kernel?
>>> scripts/faddr2line would come handy here.
>> # ./scripts/faddr2line --list vmlinux machine_kexec+0x40
>> machine_kexec+0x40/0xf8:
>>
>> machine_kexec at arch/arm/kernel/machine_kexec.c:182
>>   Â177ÂÂÂÂÂÂÂÂÂÂÂ reboot_code_buffer =
>> page_address(image->control_code_page);
>>   Â178
>>   Â179ÂÂÂÂÂÂÂÂÂÂÂ /* Prepare parameters for reboot_code_buffer*/
>>   Â180ÂÂÂÂÂÂÂÂÂÂÂ set_kernel_text_rw();
>>   Â181ÂÂÂÂÂÂÂÂÂÂÂ kexec_start_address = image->start;
>>   >182<ÂÂÂÂÂÂÂÂÂÂ kexec_indirection_page = page_list;
>>   Â183ÂÂÂÂÂÂÂÂÂÂÂ kexec_mach_type = machine_arch_type;
>>   Â184ÂÂÂÂÂÂÂÂÂÂÂ kexec_boot_atags = image->arch.kernel_r2;
>>   Â185
>>   Â186ÂÂÂÂÂÂÂÂÂÂÂ /* copy our kernel relocation code to the control code
>> page */
>>   Â187ÂÂÂÂÂÂÂÂÂÂÂ reboot_entry = fncpy(reboot_code_buffer,
> Can you please try the patch below:
>
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 963b5284d284..f86b3d17928e 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -571,7 +571,7 @@ static inline void section_update(unsigned long addr, pmdval_t mask,
>   {
>   	pmd_t *pmd;
>   
> -	pmd = pmd_off_k(addr);
> +	pmd = pmd_offset(pud_offset(p4d_offset(pgd_offset(mm, addr), addr), addr), addr);
>   
>   #ifdef CONFIG_ARM_LPAE
>   	pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
This fixes kexec issue! Thanks!


Feel free to add:

Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Fixes: 218f1c390557 ("arm: add support for folded p4d page tables")
Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>

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