Re: [PATCH] arm: mvebu: AC5/AC5X: use fixed page table size

[Marc Zyngier <maz@kernel.org>]

On 2023-10-18 21:53, Chris Packham wrote:
> Since commit 6cdf6b7a340d ("arm64: Use FEAT_HAFDBS to track dirty pages
> when available") the default get_page_table_size() sets some flags for
> more efficient handling of dirty page table entries. This causes
> problems on the AC5/AC5X SoC (specifically a lockup when calling
> __asm_switch_ttbr() via mmu_set_region_dcache_behaviour()).
> 
> The reason for the lockup isn't at all clear but it can be avoided if 
> we
> provide our own get_page_table_size() which stops gd->arch.has_hafdbs
> from being set to true effectively returning the AC5/AC5X to the older
> behaviour. This also opts for a simple fixed page table size rather 
> than
> trying to duplicate the more complicated logic to optimise the table
> size.
> 
> Signed-off-by: Chris Packham <judge.packham@gmail.com>
> ---
> 
>  arch/arm/mach-mvebu/alleycat5/cpu.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm/mach-mvebu/alleycat5/cpu.c
> b/arch/arm/mach-mvebu/alleycat5/cpu.c
> index 8204d9627515..7ba57ae75e76 100644
> --- a/arch/arm/mach-mvebu/alleycat5/cpu.c
> +++ b/arch/arm/mach-mvebu/alleycat5/cpu.c
> @@ -63,6 +63,11 @@ static struct mm_region ac5_mem_map[] = {
> 
>  struct mm_region *mem_map = ac5_mem_map;
> 
> +u64 get_page_table_size(void)
> +{
> +	return 0x80000;
> +}
> +
>  void reset_cpu(void)
>  {
>  }

This looks terribly wrong. In all honesty, if the original
patch creates problems and that people add this sort of stuff
to paper over it, I'd rather your *revert* my patch altogether.

         M.
-- 
Jazz is not dead. It just smells funny...