Re: [PATCH] sparc32: register memory occupied by kernel as memblock.memory

[Mike Rapoport <rppt@kernel.org>]

Andrew, David,

Any comments on this?

On Sun, May 24, 2020 at 07:53:58PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> sparc32 never registered the memory occupied by the kernel image with
> memblock_add() and it only reserved this memory with meblock_reserve().
> 
> With openbios as system firmware, the memory occupied by the kernel is
> reserved in openbios and removed from mem.available. The prom setup code in
> the kernel uses mem.available to set up the memory banks and essentially
> there is a hole for the memory occupied by the kernel image.
> 
> Later in bootmem_init() this memory is memblock_reserve()d.
> 
> Up until recently, memmap initialization would call __init_single_page()
> for the pages in that hole, the free_low_memory_core_early() would mark
> them as reserved and everything would be Ok.
> 
> After the change in memmap initialization introduced by the commit "mm:
> memmap_init: iterate over memblock regions rather that check each PFN", the
> hole is skipped and the page structs for it are not initialized. And when
> they are passed from memblock to page allocator as reserved, the latter
> gets confused.
> 
> Simply registering the memory occupied by the kernel with memblock_add()
> resolves this issue.
> 
> Tested on qemu-system-sparc with Debian Etch [1] userspace.
> 
> [1] https://people.debian.org/~aurel32/qemu/sparc/debian_etch_sparc_small.qcow2
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Link: https://lkml.kernel.org/r/20200517000050.GA87467@roeck-us.nlllllet/ 
> ---
> 
> David,
> 
> I'd really appreciate your Ack or an explanation where my analysis is wrong :)
> 
>  arch/sparc/mm/init_32.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/sparc/mm/init_32.c b/arch/sparc/mm/init_32.c
> index e45160839f79..eb2946b1df8a 100644
> --- a/arch/sparc/mm/init_32.c
> +++ b/arch/sparc/mm/init_32.c
> @@ -192,6 +192,7 @@ unsigned long __init bootmem_init(unsigned long *pages_avail)
>  	/* Reserve the kernel text/data/bss. */
>  	size = (start_pfn << PAGE_SHIFT) - phys_base;
>  	memblock_reserve(phys_base, size);
> +	memblock_add(phys_base, size);
>  
>  	size = memblock_phys_mem_size() - memblock_reserved_size();
>  	*pages_avail = (size >> PAGE_SHIFT) - high_pages;
> -- 
> 2.26.2
> 

-- 
Sincerely yours,
Mike.