linux-kernel - Re: [PATCH 2/5] riscv: mm: init: try best to IS_ENABLED(CONFIG

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Message-ID: <3344a7ae-aaa6-2f35-09fc-60039bb8184d@ghiti.fr>
Date:   Fri, 3 Dec 2021 09:33:12 +0100
From:   Alexandre ghiti <alex@...ti.fr>
To:     Jisheng Zhang <jszhang@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] riscv: mm: init: try best to IS_ENABLED(CONFIG_64BIT)
 instead of #ifdef

On 12/3/21 06:03, Jisheng Zhang wrote:
> Try our best to replace the conditional compilation using
> "#ifdef CONFIG_64BIT" by a check for "IS_ENABLED(CONFIG_64BIT)", to
> simplify the code and to increase compile coverage.
>
> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> ---
>   arch/riscv/mm/init.c | 38 +++++++++++++++++---------------------
>   1 file changed, 17 insertions(+), 21 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 745f26a3b02e..bd445ac778a8 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -102,10 +102,9 @@ static void __init print_vm_layout(void)
>   		  (unsigned long)VMALLOC_END);
>   	print_mlm("lowmem", (unsigned long)PAGE_OFFSET,
>   		  (unsigned long)high_memory);
> -#ifdef CONFIG_64BIT
> -	print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR,
> -		  (unsigned long)ADDRESS_SPACE_END);
> -#endif
> +	if (IS_ENABLED(CONFIG_64BIT))
> +		print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR,
> +			  (unsigned long)ADDRESS_SPACE_END);
>   }
>   #else
>   static void print_vm_layout(void) { }
> @@ -172,17 +171,16 @@ static void __init setup_bootmem(void)
>   
>   	memblock_enforce_memory_limit(memory_limit);
>   
> -	/*
> -	 * Reserve from the start of the kernel to the end of the kernel
> -	 */
> -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
>   	/*
>   	 * Make sure we align the reservation on PMD_SIZE since we will
>   	 * map the kernel in the linear mapping as read-only: we do not want
>   	 * any allocation to happen between _end and the next pmd aligned page.
>   	 */
> -	vmlinux_end = (vmlinux_end + PMD_SIZE - 1) & PMD_MASK;
> -#endif
> +	if (IS_ENABLED(CONFIG_64BIT) && IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> +		vmlinux_end = (vmlinux_end + PMD_SIZE - 1) & PMD_MASK;
> +	/*
> +	 * Reserve from the start of the kernel to the end of the kernel
> +	 */
>   	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
>   
>   
> @@ -190,7 +188,6 @@ static void __init setup_bootmem(void)
>   #ifndef CONFIG_XIP_KERNEL
>   	phys_ram_base = memblock_start_of_DRAM();
>   #endif
> -#ifndef CONFIG_64BIT
>   	/*
>   	 * memblock allocator is not aware of the fact that last 4K bytes of
>   	 * the addressable memory can not be mapped because of IS_ERR_VALUE
> @@ -200,10 +197,11 @@ static void __init setup_bootmem(void)
>   	 * address space is occupied by the kernel mapping then this check must
>   	 * be done as soon as the kernel mapping base address is determined.
>   	 */
> -	max_mapped_addr = __pa(~(ulong)0);
> -	if (max_mapped_addr == (phys_ram_end - 1))
> -		memblock_set_current_limit(max_mapped_addr - 4096);
> -#endif
> +	if (!IS_ENABLED(CONFIG_64BIT)) {
> +		max_mapped_addr = __pa(~(ulong)0);
> +		if (max_mapped_addr == (phys_ram_end - 1))
> +			memblock_set_current_limit(max_mapped_addr - 4096);
> +	}
>   
>   	min_low_pfn = PFN_UP(phys_ram_base);
>   	max_low_pfn = max_pfn = PFN_DOWN(phys_ram_end);
> @@ -616,13 +614,12 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>   	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
>   	BUG_ON((kernel_map.phys_addr % PMD_SIZE) != 0);
>   
> -#ifdef CONFIG_64BIT
>   	/*
>   	 * The last 4K bytes of the addressable memory can not be mapped because
>   	 * of IS_ERR_VALUE macro.
>   	 */
> -	BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K);
> -#endif
> +	if (IS_ENABLED(CONFIG_64BIT))
> +		BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K);


For this one, I think we can just get rid of the condition since this is 
true for every kernel actually.


>   
>   	pt_ops.alloc_pte = alloc_pte_early;
>   	pt_ops.get_pte_virt = get_pte_virt_early;
> @@ -735,10 +732,9 @@ static void __init setup_vm_final(void)
>   		}
>   	}
>   
> -#ifdef CONFIG_64BIT
>   	/* Map the kernel */
> -	create_kernel_page_table(swapper_pg_dir, false);
> -#endif
> +	if (IS_ENABLED(CONFIG_64BIT))
> +		create_kernel_page_table(swapper_pg_dir, false);


Wouldn't it be better to introduce a create_kernel_page_table function 
that does nothing for !CONFIG_64BIT?


>   
>   	/* Clear fixmap PTE and PMD mappings */
>   	clear_fixmap(FIX_PTE);