[PATCH] arm64: ignore memory outside of the linear range

[will.deacon@arm.com (Will Deacon)]

Hi Ard,

On Sat, Aug 15, 2015 at 01:13:44PM +0100, Ard Biesheuvel wrote:
> We need to ensure that we don't try to map system RAM ranges whose
> offset relative to the start of the kernel image exceeds the size of
> the linear range. This may happen even on systems that don't have
> huge amounts of RAM if it is laid out very sparsely.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> 
> This is the minimal fix for addressing the issue we discussed. I dropped
> the other changes for now, let's revisit those when (if) my patches for
> decoupling the kernel mapping from the linear mapping are back under
> discussion.
> 
> I will leave it up to the maintainers whether this constitutes a bugfix or
> not, but since this has never worked from the beginning afaict, I don't
> think it belongs in stable per se.
> 
>  arch/arm64/mm/init.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index ad87ce826cce..c65e57d4c3e7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -158,6 +158,19 @@ early_param("mem", early_mem);
>  
>  void __init arm64_memblock_init(void)
>  {
> +	/*
> +	 * Remove the memory that we will not be able to cover
> +	 * with the linear mapping.
> +	 */
> +	const s64 linear_region_size = -(s64)PAGE_OFFSET;
> +
> +	if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) {
> +		pr_warn("Ignoring memory outside of linear range (0x%012llx - 0x%012llx)\n",
> +			memstart_addr + linear_region_size,
> +			(u64)memblock_end_of_DRAM() - 1);
> +		memblock_remove(memstart_addr + linear_region_size, ULLONG_MAX);
> +	}
> +

I think this will interact badly with Mark Salter's patches to relocate
the initrd if it falls outside of the linear mapping (which relies on the
memblocks remaining intact after paging_init):

  https://lkml.org/lkml/2015/8/16/75

Some version of those patches got queued via akpm (since there is a
dependency on some generic + x86 changes), so we'd need to work out how
these two changes interact before merging this,

Will