Re: [PATCH v8 1/6] powerpc/fadump: reduce memory consumption for capture kernel

[Hari Bathini <hbathini@linux.vnet.ibm.com>]

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On Tuesday 12 September 2017 09:31 PM, Michal Suchanek wrote:
> With fadump (dump capture) kernel booting like a regular kernel, it needs
> almost the same amount of memory to boot as the production kernel, which is
> unwarranted for a dump capture kernel. But with no option to disable some
> of the unnecessary subsystems in fadump kernel, that much memory is wasted
> on fadump, depriving the production kernel of that memory.
>
> Introduce kernel parameter 'fadump_extra_args=' that would take regular
> parameters as a space separated quoted string, to be enforced when fadump
> is active. This 'fadump_extra_args=' parameter can be leveraged to pass
> parameters like nr_cpus=1, cgroup_disable=memory and numa=off, to disable
> unwarranted resources/subsystems.
>
> Also, ensure the log "Firmware-assisted dump is active" is printed early
> in the boot process to put the subsequent fadump messages in context.
>
> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>

For the series...

Tested-by: Hari Bathini <hbathini@linux.vnet.ibm.com>

> ---
> Changes from v6:
> Correct and simplify quote handling. Ideally I would like to extend
> parse_args to give the length of the original quoted value to callback.
> However, parse_args removes at most one doubel-quote from the start and
> one from the end so that is easy to detect. Otherwise all other users
> will have to be updated to trash the new argument.
> Changes from v7:
> Handle leading quote in parameter name.
> ---
>   arch/powerpc/include/asm/fadump.h |   2 +
>   arch/powerpc/kernel/fadump.c      | 122 +++++++++++++++++++++++++++++++++++++-
>   arch/powerpc/kernel/prom.c        |   7 +++
>   3 files changed, 128 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/fadump.h b/arch/powerpc/include/asm/fadump.h
> index 5a23010af600..41b50b317a67 100644
> --- a/arch/powerpc/include/asm/fadump.h
> +++ b/arch/powerpc/include/asm/fadump.h
> @@ -208,12 +208,14 @@ extern int early_init_dt_scan_fw_dump(unsigned long node,
>   		const char *uname, int depth, void *data);
>   extern int fadump_reserve_mem(void);
>   extern int setup_fadump(void);
> +extern void enforce_fadump_extra_args(char *cmdline);
>   extern int is_fadump_active(void);
>   extern int should_fadump_crash(void);
>   extern void crash_fadump(struct pt_regs *, const char *);
>   extern void fadump_cleanup(void);
>
>   #else	/* CONFIG_FA_DUMP */
> +static inline void enforce_fadump_extra_args(char *cmdline) { }
>   static inline int is_fadump_active(void) { return 0; }
>   static inline int should_fadump_crash(void) { return 0; }
>   static inline void crash_fadump(struct pt_regs *regs, const char *str) { }
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index e1431800bfb9..0e08f1a80af2 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -78,8 +78,10 @@ int __init early_init_dt_scan_fw_dump(unsigned long node,
>   	 * dump data waiting for us.
>   	 */
>   	fdm_active = of_get_flat_dt_prop(node, "ibm,kernel-dump", NULL);
> -	if (fdm_active)
> +	if (fdm_active) {
> +		pr_info("Firmware-assisted dump is active.\n");
>   		fw_dump.dump_active = 1;
> +	}
>
>   	/* Get the sizes required to store dump data for the firmware provided
>   	 * dump sections.
> @@ -339,8 +341,11 @@ int __init fadump_reserve_mem(void)
>   {
>   	unsigned long base, size, memory_boundary;
>
> -	if (!fw_dump.fadump_enabled)
> +	if (!fw_dump.fadump_enabled) {
> +		if (fw_dump.dump_active)
> +			pr_warn("Firmware-assisted dump was active but kernel booted with fadump disabled!\n");
>   		return 0;
> +	}
>
>   	if (!fw_dump.fadump_supported) {
>   		printk(KERN_INFO "Firmware-assisted dump is not supported on"
> @@ -380,7 +385,6 @@ int __init fadump_reserve_mem(void)
>   		memory_boundary = memblock_end_of_DRAM();
>
>   	if (fw_dump.dump_active) {
> -		printk(KERN_INFO "Firmware-assisted dump is active.\n");
>   		/*
>   		 * If last boot has crashed then reserve all the memory
>   		 * above boot_memory_size so that we don't touch it until
> @@ -467,6 +471,118 @@ static int __init early_fadump_reserve_mem(char *p)
>   }
>   early_param("fadump_reserve_mem", early_fadump_reserve_mem);
>
> +#define FADUMP_EXTRA_ARGS_PARAM		"fadump_extra_args="
> +#define FADUMP_EXTRA_ARGS_LEN		(strlen(FADUMP_EXTRA_ARGS_PARAM) - 1)
> +
> +struct param_info {
> +	char		*cmdline;
> +	char		*tmp_cmdline;
> +	int		 shortening;
> +};
> +
> +static void __init fadump_update_params(struct param_info *param_info,
> +					char *param, char *val)
> +{
> +	ptrdiff_t param_offset = param - param_info->tmp_cmdline;
> +	size_t vallen = val ? strlen(val) : 0;
> +	char *tgt = param_info->cmdline + param_offset
> +				- param_info->shortening;
> +	int shortening = 0;
> +	int quoted = 0;
> +
> +	if (!val)
> +		return;
> +
> +	/* leading '"' removed from parameter */
> +	if ((param > param_info->tmp_cmdline) && *(param - 1) == '"') {
> +		quoted = 1;
> +		shortening += 1;
> +		tgt--;
> +	}
> +
> +	/* next_arg removes one leading and one trailing '"' */
> +	if (*(tgt + FADUMP_EXTRA_ARGS_LEN + 1) == '"')
> +		shortening += 1;
> +	if (*(tgt + FADUMP_EXTRA_ARGS_LEN + 1 + vallen + shortening) == '"')
> +		shortening += 1;
> +
> +	/* remove one leading and one trailing quote if both are present */
> +	if ((val[0] == '"') && (val[vallen - 1] == '"')) {
> +		shortening += 2;
> +		vallen -= 2;
> +		val++;
> +	}
> +
> +	/* some characters were removed - move the trailing part of cmdline */
> +	if (shortening) {
> +		char *src;
> +
> +		strncpy(tgt, FADUMP_EXTRA_ARGS_PARAM, FADUMP_EXTRA_ARGS_LEN);
> +		tgt += FADUMP_EXTRA_ARGS_LEN;
> +		*tgt++ = ' ';
> +
> +		strncpy(tgt, val, vallen);
> +		tgt += vallen;
> +
> +		src = tgt + shortening;
> +		memmove(tgt, src, strlen(src) + 1);
> +	} else {
> +		/* remove the '=' */
> +		*(tgt + FADUMP_EXTRA_ARGS_LEN) = ' ';
> +	}
> +
> +	param_info->shortening += shortening;
> +}
> +
> +/*
> + * Reworks command line parameters and splits 'fadump_extra_args=' param
> + * to enforce the parameters passed through it
> + */
> +static int __init fadump_rework_cmdline_params(char *param, char *val,
> +					       const char *unused, void *arg)
> +{
> +	struct param_info *param_info = (struct param_info *)arg;
> +
> +	if (strncmp(param, FADUMP_EXTRA_ARGS_PARAM,
> +		     strlen(FADUMP_EXTRA_ARGS_PARAM) - 1))
> +		return 0;
> +
> +	fadump_update_params(param_info, param, val);
> +
> +	return 0;
> +}
> +
> +/*
> + * Replace every occurrence of 'fadump_extra_args="param1 param2 param3"'
> + * in cmdline with 'fadump_extra_args param1 param2 param3' by stripping
> + * off '=' and quotes, if any. This ensures that the additional parameters
> + * passed with 'fadump_extra_args=' are enforced.
> + */
> +void __init enforce_fadump_extra_args(char *cmdline)
> +{
> +	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> +	static char init_cmdline[COMMAND_LINE_SIZE] __initdata;
> +	struct param_info param_info;
> +
> +	if (strstr(cmdline, FADUMP_EXTRA_ARGS_PARAM) == NULL)
> +		return;
> +
> +	pr_info("Modifying command line to enforce the additional parameters passed through 'fadump_extra_args='");
> +
> +	param_info.cmdline = cmdline;
> +	param_info.tmp_cmdline = tmp_cmdline;
> +	param_info.shortening = 0;
> +
> +	strlcpy(init_cmdline, cmdline, COMMAND_LINE_SIZE);
> +
> +	strlcpy(tmp_cmdline, cmdline, COMMAND_LINE_SIZE);
> +	parse_args("fadump params", tmp_cmdline, NULL, 0, 0, 0,
> +			&param_info, &fadump_rework_cmdline_params);
> +
> +	pr_info("Original command line: %s\n", init_cmdline);
> +	pr_info("Modified command line: %s\n", cmdline);
> +}
> +
>   static int register_fw_dump(struct fadump_mem_struct *fdm)
>   {
>   	int rc, err;
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index f83056297441..2e6f40217266 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -693,6 +693,13 @@ void __init early_init_devtree(void *params)
>   	of_scan_flat_dt(early_init_dt_scan_root, NULL);
>   	of_scan_flat_dt(early_init_dt_scan_memory_ppc, NULL);
>
> +	/*
> +	 * Look for 'fadump_extra_args=' parameter and enfore the additional
> +	 * parameters passed to it if fadump is active.
> +	 */
> +	if (is_fadump_active())
> +		enforce_fadump_extra_args(boot_command_line);
> +
>   	parse_early_param();
>
>   	/* make sure we've parsed cmdline for mem= before this */


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