linux-kernel - Re: [PATCH 02/22] ARM: use late patch framework for phys-virt patching

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Message-ID: <alpine.LFD.2.02.1208040138560.5231@xanadu.home>
Date:	Sat, 4 Aug 2012 02:15:56 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Cyril Chemparathy <cyril@...com>
cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, catalin.marinas@....com, linux@....linux.org.uk,
	will.deacon@....com
Subject: Re: [PATCH 02/22] ARM: use late patch framework for phys-virt
 patching

On Tue, 31 Jul 2012, Cyril Chemparathy wrote:

> This patch replaces the original physical offset patching implementation
> with one that uses the newly added patching framework.  In the process, we now
> unconditionally initialize the __pv_phys_offset and __pv_offset globals in the
> head.S code.

Why unconditionally initializing those?  There is no reason for that.

> Signed-off-by: Cyril Chemparathy <cyril@...com>

Comments below.

> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 835898e..d165896 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
[...]
>  	.data
>  	.globl	__pv_phys_offset
>  	.type	__pv_phys_offset, %object
>  __pv_phys_offset:
>  	.long	0
>  	.size	__pv_phys_offset, . - __pv_phys_offset
> +
> +	.globl	__pv_offset
> +	.type	__pv_offset, %object
>  __pv_offset:
>  	.long	0
> -#endif
> +	.size	__pv_offset, . - __pv_offset

Please move those to C code.  They aren't of much use in this file 
anymore.  This will allow you to use pphys_addr_t for them as well in 
your subsequent patch. And more importantly get rid of that ugly 
pv_offset_high that you introduced iin another patch.

> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> index df5e897..39f8fce 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -317,11 +317,6 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
>  					         maps[i].txt_sec->sh_addr,
>  					         maps[i].txt_sec->sh_size);
>  #endif
> -#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
> -	s = find_mod_section(hdr, sechdrs, ".pv_table");
> -	if (s)
> -		fixup_pv_table((void *)s->sh_addr, s->sh_size);
> -#endif
>  	s = find_mod_section(hdr, sechdrs, ".patch.table");
>  	if (s)
>  		patch_kernel((void *)s->sh_addr, s->sh_size);

The patch_kernel code and its invokation should still be conditional on 
CONFIG_ARM_PATCH_PHYS_VIRT.  This ability may still be configured out 
irrespective of the implementation used.

> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index bacb275..13731e3 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -162,11 +162,6 @@ SECTIONS
>  		__smpalt_end = .;
>  	}
>  #endif
> -	.init.pv_table : {
> -		__pv_table_begin = .;
> -		*(.pv_table)
> -		__pv_table_end = .;
> -	}
>  	.init.patch_table : {
>  		__patch_table_begin = .;
>  		*(.patch.table)

Since you're changing the module ABI,it is important to also modify the 
module vermagic string in asm/module.h to prevent the loading of 
incompatible kernel modules.


Nicolas
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