linux-kernel - Re: [PATCH v3 1/3] riscv: Factorize xip and !xip kernel address conversion macros

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Date:   Thu, 3 Jun 2021 20:27:48 +0800
From:   Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jisheng Zhang <jszhang@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Zong Li <zong.li@...ive.com>, Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] riscv: Factorize xip and !xip kernel address
 conversion macros

On Thu,  3 Jun 2021 10:27:47 +0200
Alexandre Ghiti <alex@...ti.fr> wrote:

> To simplify the kernel address conversion code, make the same definition of
> kernel_mapping_pa_to_va and kernel_mapping_va_to_pa compatible for both xip
> and !xip kernel by defining XIP_OFFSET to 0 in !xip kernel.
> 
> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
> ---
>  arch/riscv/include/asm/page.h    | 14 +++-----------
>  arch/riscv/include/asm/pgtable.h |  2 ++
>  2 files changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 6a7761c86ec2..6e004d8fda4d 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -93,9 +93,7 @@ extern unsigned long va_pa_offset;
>  #ifdef CONFIG_64BIT
>  extern unsigned long va_kernel_pa_offset;
>  #endif
> -#ifdef CONFIG_XIP_KERNEL
>  extern unsigned long va_kernel_xip_pa_offset;
> -#endif
>  extern unsigned long pfn_base;
>  #define ARCH_PFN_OFFSET		(pfn_base)
>  #else
> @@ -103,6 +101,7 @@ extern unsigned long pfn_base;
>  #ifdef CONFIG_64BIT
>  #define va_kernel_pa_offset	0
>  #endif
> +#define va_kernel_xip_pa_offset 0
>  #define ARCH_PFN_OFFSET		(PAGE_OFFSET >> PAGE_SHIFT)
>  #endif /* CONFIG_MMU */
>  
> @@ -110,29 +109,22 @@ extern unsigned long kernel_virt_addr;
>  
>  #ifdef CONFIG_64BIT
>  #define linear_mapping_pa_to_va(x)	((void *)((unsigned long)(x) + va_pa_offset))
> -#ifdef CONFIG_XIP_KERNEL
>  #define kernel_mapping_pa_to_va(y)	({						\
>  	unsigned long _y = y;								\
>  	(_y >= CONFIG_PHYS_RAM_BASE) ?	

This CONFIG_PHYS_RAM_BASE is only available for XIP, could result in a
compiler error for !XIP?

I'm also concerned with the unecessary overhead of kernel_mapping_pa_to_va()
for !XIP case, there's a "if" condition branch, and extra symbol: va_kernel_xip_pa_offset

>  		(void *)((unsigned long)(_y) + va_kernel_pa_offset + XIP_OFFSET) :	\
>  		(void *)((unsigned long)(_y) + va_kernel_xip_pa_offset);		\
>  	})
> -#else
> -#define kernel_mapping_pa_to_va(x)	((void *)((unsigned long)(x) + va_kernel_pa_offset))
> -#endif
>  #define __pa_to_va_nodebug(x)		linear_mapping_pa_to_va(x)
>  
>  #define linear_mapping_va_to_pa(x)	((unsigned long)(x) - va_pa_offset)
> -#ifdef CONFIG_XIP_KERNEL
>  #define kernel_mapping_va_to_pa(y) ({						\
>  	unsigned long _y = y;							\
>  	(_y < kernel_virt_addr + XIP_OFFSET) ?					\
>  		((unsigned long)(_y) - va_kernel_xip_pa_offset) :		\
>  		((unsigned long)(_y) - va_kernel_pa_offset - XIP_OFFSET);	\
>  	})

Similar as kernel_mapping_pa_to_va(), an overhead of "if" condition branch
for !XIP and extra va_kernel_xip_pa_offset symbol.

> -#else
> -#define kernel_mapping_va_to_pa(x)	((unsigned long)(x) - va_kernel_pa_offset)
> -#endif
> +
>  #define __va_to_pa_nodebug(x)	({						\
>  	unsigned long _x = x;							\
>  	(_x < kernel_virt_addr) ?						\
> @@ -141,7 +133,7 @@ extern unsigned long kernel_virt_addr;
>  #else
>  #define __pa_to_va_nodebug(x)  ((void *)((unsigned long) (x) + va_pa_offset))
>  #define __va_to_pa_nodebug(x)  ((unsigned long)(x) - va_pa_offset)
> -#endif
> +#endif /* CONFIG_64BIT */
>  
>  #ifdef CONFIG_DEBUG_VIRTUAL
>  extern phys_addr_t __virt_to_phys(unsigned long x);
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index bde8ce3bfe7c..d98e931a31e5 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -77,6 +77,8 @@
>  
>  #ifdef CONFIG_XIP_KERNEL
>  #define XIP_OFFSET		SZ_8M
> +#else
> +#define XIP_OFFSET		0
>  #endif
>  
>  #ifndef __ASSEMBLY__