Re: [PATCH v2] ARC: Use max_high_pfn as a HIGHMEM zone border

[Vineet Gupta <Vineet.Gupta1@synopsys.com>]

On 4/27/21 5:13 AM, Vladimir Isaev wrote:
> Commit 4af22ded0ecf ("arc: fix memory initialization for systems
> with two memory banks") fixed highmem, but for the PAE case it causes
> bug messages:
>
> BUG: Bad page state in process swapper  pfn:80000
> page:(ptrval) refcount:0 mapcount:1 mapping:00000000 index:0x0 pfn:0x80000
> flags: 0x0()
> raw: 00000000 00000100 00000122 00000000 00000000 00000000 00000000 00000000
> raw: 00000000
> page dumped because: nonzero mapcount
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.12.0-rc5-00003-g1e43c377a79f #1
>
> Stack Trace:
>    arc_unwind_core+0xe8/0x118
> Disabling lock debugging due to kernel taint
>
> This is because the fix expects highmem to be always less than
> lowmem and uses min_low_pfn as an upper zone border for highmem.
>
> max_high_pfn should be ok for both highmem and highmem+PAE cases.
>
> Signed-off-by: Vladimir Isaev <isaev@synopsys.com>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: Vineet Gupta <vgupta@synopsys.com>

Applied to for-curr.

Thx,
-Vineet

> ---
> Changes for v2:
>   - Revised commit message and added comment to code
> ---
>   arch/arc/mm/init.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
> index ce07e697916c..1bcc6985b9a0 100644
> --- a/arch/arc/mm/init.c
> +++ b/arch/arc/mm/init.c
> @@ -157,7 +157,16 @@ void __init setup_arch_memory(void)
>   	min_high_pfn = PFN_DOWN(high_mem_start);
>   	max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);
>   
> -	max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> +	/*
> +	 * max_high_pfn should be ok here for both HIGHMEM and HIGHMEM+PAE.
> +	 * For HIGHMEM without PAE max_high_pfn should be less than
> +	 * min_low_pfn to guarantee that these two regions don't overlap.
> +	 * For PAE case highmem is greater than lowmem, so it is natural
> +	 * to use max_high_pfn.
> +	 *
> +	 * In both cases, holes should be handled by pfn_valid().
> +	 */
> +	max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
>   
>   	high_memory = (void *)(min_high_pfn << PAGE_SHIFT);
>