linux-kernel - Re: [PATCH] MCA: garbage collect sys_desc

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Date:	Thu, 16 Jul 2015 18:13:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Paolo Pisati <p.pisati@...il.com>
cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	josh@...htriplett.org
Subject: Re: [PATCH] MCA: garbage collect sys_desc_table

On Wed, 8 Jul 2015, Paolo Pisati wrote:

This lacks a proper changelog.

> Signed-off-by: Paolo Pisati <p.pisati@...il.com>
> diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt
> index 82fbdbc..0761737 100644
> --- a/Documentation/x86/zero-page.txt
> +++ b/Documentation/x86/zero-page.txt
> @@ -17,7 +17,6 @@ Offset	Proto	Name		Meaning
>  				(struct ist_info)
>  080/010	ALL	hd0_info	hd0 disk parameter, OBSOLETE!!
>  090/010	ALL	hd1_info	hd1 disk parameter, OBSOLETE!!
> -0A0/010	ALL	sys_desc_table	System description table (struct sys_desc_table)

Removing this is wrong. The space stays reserved for sys_desc_table.
It's just unused and should be marked OBSOLETE.

>  extern void set_task_blockstep(struct task_struct *task, bool on);
>  
> -/*
> - * from system description table in BIOS. Mostly for MCA use, but
> - * others may find it useful:
> - */
> -extern unsigned int		machine_id;
> -extern unsigned int		machine_submodel_id;
> -extern unsigned int		BIOS_revision;
> -
>  /* Boot loader type from the setup header: */
>  extern int			bootloader_type;
>  extern int			bootloader_version;
> diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
> index ab456dc..ad00cf4 100644
> --- a/arch/x86/include/uapi/asm/bootparam.h
> +++ b/arch/x86/include/uapi/asm/bootparam.h
> @@ -86,11 +86,6 @@ struct setup_header {
>  	__u32	handover_offset;
>  } __attribute__((packed));
>  
> -struct sys_desc_table {
> -	__u16 length;
> -	__u8  table[14];
> -};
> -
>  /* Gleaned from OFW's set-parameters in cpu/x86/pc/linux.fth */
>  struct olpc_ofw_header {
>  	__u32 ofw_magic;	/* OFW signature */
> @@ -120,12 +115,12 @@ struct boot_params {
>  	__u8  _pad3[16];				/* 0x070 */
>  	__u8  hd0_info[16];	/* obsolete! */		/* 0x080 */
>  	__u8  hd1_info[16];	/* obsolete! */		/* 0x090 */
> -	struct sys_desc_table sys_desc_table;		/* 0x0a0 */
> +	__u8  _pad4[16];					/* 0x0a0 */

This is a UAPI header and we dont know what might reference that
field. Leave it as is and mark it obsolete.

> --- a/arch/x86/kernel/kexec-bzimage64.c
> +++ b/arch/x86/kernel/kexec-bzimage64.c
> @@ -222,9 +222,6 @@ setup_boot_parameters(struct kimage *image, struct boot_params *params,
>  	memset(&params->hd0_info, 0, sizeof(params->hd0_info));
>  	memset(&params->hd1_info, 0, sizeof(params->hd1_info));

These two lines are useless as well, but that should be a separate patch

> -	/* Default sysdesc table */
> -	params->sys_desc_table.length = 0;
> -

Thanks,

	tglx
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