Re: [PATCH 2/5] riscv: mm: init: try best to IS_ENABLED(CONFIG_64BIT) instead of #ifdef

[Jisheng Zhang <jszhang@kernel.org>]

On Fri, 3 Dec 2021 09:33:12 +0100
Alexandre ghiti <alex@ghiti.fr> wrote:

> 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@kernel.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.

Thanks for pointing out this out. Addressed in v2

> 
> 
> >   
> >   	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?
> 

If so, we will have something as:
#ifdef CONFIG_64BIT
create_kernel_page_table()
{
...
}
#else
create_kernel_page_table() { }
#endif

Since we already have different create_kernel_page_table() version for
XIP and !XIP, the code would be more complex.

Thanks for your code review