[PATCH 1/3] riscv: Fix memory_limit for 64-bit kernel

[Kefeng Wang]

On 2021/6/29 17:13, Alexandre Ghiti wrote:
> As described in Documentation/riscv/vm-layout.rst, the end of the
> virtual address space for 64-bit kernel is occupied by the modules/BPF/
> kernel mappings so this actually reduces the amount of memory we are able
> to map and then use in the linear mapping. So make sure this limit is
> correctly set.
>
> Fixes: c9811e379b21 ("riscv: Add mem kernel parameter support")


Should the Fixes tag be de043da0b9e7 （“RISC-V: Fix usage of 
memblock_enforce_memory_limit“）,

The -PAGE_OFFSET is set to the maximal physical memory from this point :)

> Signed-off-by: Alexandre Ghiti <alex at ghiti.fr>
> ---
>   arch/riscv/mm/init.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 12f956b3a674..04a5db3a9788 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -124,10 +124,17 @@ void __init mem_init(void)
>   }
>   
>   /*
> - * The default maximal physical memory size is -PAGE_OFFSET,
> - * limit the memory size via mem.
> + * The default maximal physical memory size is -PAGE_OFFSET for 32-bit kernel,
> + * whereas for 64-bit kernel, the end of the virtual address space is occupied
> + * by the modules/BPF/kernel mappings which reduces the available size of the
> + * linear mapping.
> + * Limit the memory size via mem.
>    */
> +#ifdef CONFIG_64BIT
> +static phys_addr_t memory_limit = -PAGE_OFFSET - SZ_4G;
> +#else
>   static phys_addr_t memory_limit = -PAGE_OFFSET;
> +#endif
>   
>   static int __init early_mem(char *p)
>   {