linux-kernel - Re: [PATCH 2/7] riscv: replace va_kernel_pa_offset with va_kernel_data_pa

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Message-ID: <335c8f7e-cef7-483c-bab7-6110e5d31071@ghiti.fr>
Date: Mon, 27 May 2024 14:32:58 +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 2/7] riscv: replace va_kernel_pa_offset with
 va_kernel_data_pa_offset on XIP


On 10/05/2024 08:28, Nam Cao wrote:
> On XIP kernel, the name "va_kernel_pa_offset" is misleading: unlike
> "normal" kernel, it is not the virtual-physical address offset of kernel
> mapping, it is the offset of kernel mapping's first virtual address to
> first physical address in DRAM, which is not meaningful because the
> kernel's first physical address is not in DRAM.
>
> For XIP kernel, there are 2 different offsets because the read-only part of
> the kernel resides in ROM while the rest is in RAM. The offset to ROM is in
> kernel_map.va_kernel_xip_pa_offset, while the offset to RAM is not stored
> anywhere: it is calculated on-the-fly.
>
> Remove this confusing "va_kernel_pa_offset" and add
> "va_kernel_data_pa_offset" as its replacement. This new variable is the
> offset of virtual mapping of the kernel's data portion to the corresponding
> physical addresses.
>
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> ---
>   arch/riscv/include/asm/page.h | 25 +++++++++++++++++++------
>   arch/riscv/mm/init.c          |  4 +++-
>   2 files changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 115ac98b8d72..14d0de928f9b 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -112,11 +112,13 @@ struct kernel_mapping {
>   	/* Offset between linear mapping virtual address and kernel load address */
>   	unsigned long va_pa_offset;
>   	/* Offset between kernel mapping virtual address and kernel load address */
> -	unsigned long va_kernel_pa_offset;
> -	unsigned long va_kernel_xip_pa_offset;
>   #ifdef CONFIG_XIP_KERNEL
> +	unsigned long va_kernel_xip_pa_offset;
> +	unsigned long va_kernel_data_pa_offset;


I would call that new field va_kernel_xip_data_pa_offset so that we know 
at first sight it only applies to XIP_KERNEL (and maybe rename 
va_kernel_xip_pa_offset into va_kernel_xip_text_pa_offset?).


>   	uintptr_t xiprom;
>   	uintptr_t xiprom_sz;
> +#else
> +	unsigned long va_kernel_pa_offset;
>   #endif
>   };
>   
> @@ -134,12 +136,18 @@ extern phys_addr_t phys_ram_base;
>   #else
>   void *linear_mapping_pa_to_va(unsigned long x);
>   #endif
> +
> +#ifdef CONFIG_XIP_KERNEL
>   #define kernel_mapping_pa_to_va(y)	({					\
>   	unsigned long _y = (unsigned long)(y);					\
> -	(IS_ENABLED(CONFIG_XIP_KERNEL) && _y < phys_ram_base) ?			\
> +	(_y < phys_ram_base) ?							\
>   		(void *)(_y + kernel_map.va_kernel_xip_pa_offset) :		\
> -		(void *)(_y + kernel_map.va_kernel_pa_offset + XIP_OFFSET);	\
> +		(void *)(_y + kernel_map.va_kernel_data_pa_offset);		\
>   	})
> +#else
> +#define kernel_mapping_pa_to_va(y) (void *)((unsigned long)(y) + kernel_map.va_kernel_pa_offset)
> +#endif
> +
>   #define __pa_to_va_nodebug(x)		linear_mapping_pa_to_va(x)
>   
>   #ifndef CONFIG_DEBUG_VIRTUAL
> @@ -147,12 +155,17 @@ void *linear_mapping_pa_to_va(unsigned long x);
>   #else
>   phys_addr_t linear_mapping_va_to_pa(unsigned long x);
>   #endif
> +
> +#ifdef CONFIG_XIP_KERNEL
>   #define kernel_mapping_va_to_pa(y) ({						\
>   	unsigned long _y = (unsigned long)(y);					\
> -	(IS_ENABLED(CONFIG_XIP_KERNEL) && _y < kernel_map.virt_addr + XIP_OFFSET) ? \
> +	(_y < kernel_map.virt_addr + XIP_OFFSET) ?				\
>   		(_y - kernel_map.va_kernel_xip_pa_offset) :			\
> -		(_y - kernel_map.va_kernel_pa_offset - XIP_OFFSET);		\
> +		(_y - kernel_map.va_kernel_data_pa_offset);			\
>   	})
> +#else
> +#define kernel_mapping_va_to_pa(y) ((unsigned long)(y) - kernel_map.va_kernel_pa_offset)
> +#endif
>   
>   #define __va_to_pa_nodebug(x)	({						\
>   	unsigned long _x = x;							\
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 5e3ec076ab95..9846c6924509 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -1089,10 +1089,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>   	kernel_map.size = (uintptr_t)(&_end) - (uintptr_t)(&_start);
>   
>   	kernel_map.va_kernel_xip_pa_offset = kernel_map.virt_addr - kernel_map.xiprom;
> +	kernel_map.va_kernel_data_pa_offset = kernel_map.virt_addr - kernel_map.phys_addr
> +						+ (uintptr_t)&_sdata - (uintptr_t)&_start;
>   #else
>   	kernel_map.page_offset = _AC(CONFIG_PAGE_OFFSET, UL);
>   	kernel_map.phys_addr = (uintptr_t)(&_start);
>   	kernel_map.size = (uintptr_t)(&_end) - kernel_map.phys_addr;
> +	kernel_map.va_kernel_pa_offset = kernel_map.virt_addr - kernel_map.phys_addr;
>   #endif
>   
>   #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL)
> @@ -1114,7 +1117,6 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>   	 */
>   	kernel_map.va_pa_offset = IS_ENABLED(CONFIG_64BIT) ?
>   				0UL : PAGE_OFFSET - kernel_map.phys_addr;
> -	kernel_map.va_kernel_pa_offset = kernel_map.virt_addr - kernel_map.phys_addr;
>   
>   	/*
>   	 * The default maximal physical memory size is KERN_VIRT_SIZE for 32-bit


I think you missed the occurence of va_kernel_pa_offset() in 
arch/riscv/kernel/vmcore_info.c.

Although some nits above, you can add:

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

Thanks,

Alex