linux-kernel - Re: [PATCH 6/7] riscv: drop the use of XIP_OFFSET in create_kernel_page

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Date: Mon, 27 May 2024 14:53:29 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Nam Cao <namcao@...utronix.de>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] riscv: drop the use of XIP_OFFSET in
 create_kernel_page_table()


On 10/05/2024 08:28, Nam Cao wrote:
> XIP_OFFSET is the hard-coded offset of writable data section within the
> kernel.
>
> By hard-coding this value, the read-only section of the kernel (which is
> placed before the writable data section) is restricted in size.
>
> As a preparation to remove this hard-coded value entirely, stop using
> XIP_OFFSET in create_kernel_page_table(). Instead use _sdata and _start to
> do the same thing.
>
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> ---
>   arch/riscv/mm/init.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 9846c6924509..62ff4aa2be96 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -907,7 +907,7 @@ static void __init relocate_kernel(void)
>   static void __init create_kernel_page_table(pgd_t *pgdir,
>   					    __always_unused bool early)
>   {
> -	uintptr_t va, end_va;
> +	uintptr_t va, start_va, end_va;
>   
>   	/* Map the flash resident part */
>   	end_va = kernel_map.virt_addr + kernel_map.xiprom_sz;
> @@ -917,10 +917,11 @@ static void __init create_kernel_page_table(pgd_t *pgdir,
>   				   PMD_SIZE, PAGE_KERNEL_EXEC);
>   
>   	/* Map the data in RAM */
> +	start_va = kernel_map.virt_addr + (uintptr_t)&_sdata - (uintptr_t)&_start;
>   	end_va = kernel_map.virt_addr + kernel_map.size;
> -	for (va = kernel_map.virt_addr + XIP_OFFSET; va < end_va; va += PMD_SIZE)
> +	for (va = start_va; va < end_va; va += PMD_SIZE)
>   		create_pgd_mapping(pgdir, va,
> -				   kernel_map.phys_addr + (va - (kernel_map.virt_addr + XIP_OFFSET)),
> +				   kernel_map.phys_addr + (va - start_va),
>   				   PMD_SIZE, PAGE_KERNEL);
>   }
>   #else


Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex