[PATCH] arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required

[Anshuman Khandual]

On 11/19/20 11:25 PM, Catalin Marinas wrote:
> mem_init() currently relies on knowing the boundaries of the crashkernel
> reservation to map such region with page granularity for later
> unmapping via set_memory_valid(..., 0). If the crashkernel reservation
> is deferred, such boundaries are not known when the linear mapping is
> created. Simply parse the command line for "crashkernel" and, if found,
> create the linear map with NO_BLOCK_MAPPINGS.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> Cc: James Morse <james.morse at arm.com>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>
> ---
> 
> Following the online (and offline) discussion with James and Nicolas,
> this aims to avoid issues with moving the reserve_crashkernel() call to
> after the memory map has been created (the ZONE_DMA patches).
> 
> https://lore.kernel.org/r/e60d643e-4879-3fc3-737d-2c145332a6d7@arm.com
> 
>  arch/arm64/mm/mmu.c | 37 ++++++++++++++++---------------------
>  1 file changed, 16 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index d7fe72ee678a..dd214157a026 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -469,6 +469,21 @@ void __init mark_linear_text_alias_ro(void)
>  			    PAGE_KERNEL_RO);
>  }
>  
> +static bool crash_mem_map __initdata;
> +
> +static int __init enable_crash_mem_map(char *arg)
> +{
> +	/*
> +	 * Proper parameter parsing is done by reserve_crashkernel(). We only
> +	 * need to know if the linear map has to avoid block mappings so that
> +	 * the crashkernel reservations can be unmapped later.
> +	 */
> +	crash_mem_map = true;
> +
> +	return 0;
> +}
> +early_param("crashkernel", enable_crash_mem_map);

Should not the crash kernel cmdline parameter gets parsed enough, just to
ensure it is atleast a valid one ? Otherwise an invalid cmdline request
can prevent the block mapping. In that case, the kernel will neither have
a crash kernel nor the block mapping.