Re: [RFC v4 PATCH 4/5] powerpc/crash hp: add crash hotplug support for kexec_file_load

[Laurent Dufour <ldufour@linux.ibm.com>]

On 11/04/2022, 10:43:56, Sourabh Jain wrote:
> Two major changes are done to enable the crash CPU hotplug handler.
> Firstly, updated the kexec load path to prepare kimage for hotplug
> changes, and secondly, implemented the crash hotplug handler.
> 
> On the kexec load path, the memsz allocation of the crash FDT segment
> is updated to ensure that it has sufficient buffer space to accommodate
> future hot add CPUs. Initialized the kimage members to track the kexec
> FDT segment.
> 
> The crash hotplug handler updates the cpus node of crash FDT. While we
> update crash FDT the kexec_crash_image is marked invalid and restored
> after FDT update to avoid race.
> 
> Since memory crash hotplug support is not there yet the crash hotplug
> the handler simply warns the user and returns.
> 
> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> ---
>  arch/powerpc/kexec/core_64.c | 46 ++++++++++++++++++++++
>  arch/powerpc/kexec/elf_64.c  | 74 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 120 insertions(+)
> 
> diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c
> index 249d2632526d..62f77cc86407 100644
> --- a/arch/powerpc/kexec/core_64.c
> +++ b/arch/powerpc/kexec/core_64.c
> @@ -466,6 +466,52 @@ int update_cpus_node(void *fdt)
>  	return ret;
>  }
>  
> +#ifdef CONFIG_CRASH_HOTPLUG
> +/**
> + * arch_crash_hotplug_handler() - Handle hotplug FDT changes
> + * @image: the active struct kimage
> + * @hp_action: the hot un/plug action being handled
> + * @a: first parameter dependent upon hp_action
> + * @b: first parameter dependent upon hp_action
> + *
> + * To accurately reflect CPU hot un/plug changes, the FDT
> + * must be updated with the new list of CPUs and memories.
> + */
> +void arch_crash_hotplug_handler(struct kimage *image, unsigned int hp_action,
> +				unsigned long a, unsigned long b)
> +{
> +	void *fdt;
> +
> +	/* No action needed for CPU hot-unplug */
> +	if (hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> +		return;

I should have report since in the previous version too, why nothing is done
when CPU are removed?

> +
> +	/* crash update on memory hotplug is not support yet */
> +	if (hp_action == KEXEC_CRASH_HP_REMOVE_MEMORY || hp_action == KEXEC_CRASH_HP_ADD_MEMORY) {
> +		pr_info_once("crash hp: crash update is not supported with memory hotplug\n");
> +		return;
> +	}
> +
> +	/* Must have valid FDT index */
> +	if (!image->arch.fdt_index_valid) {
> +		pr_err("crash hp: unable to locate FDT segment");
> +		return;
> +	}
> +
> +	fdt = __va((void *)image->segment[image->arch.fdt_index].mem);
> +
> +	/* Temporarily invalidate the crash image while it is replaced */
> +	xchg(&kexec_crash_image, NULL);
> +
> +	/* update FDT to refelect changes to CPU resrouces */
> +	if (update_cpus_node(fdt))
> +		pr_err("crash hp: failed to update crash FDT");
> +
> +	/* The crash image is now valid once again */
> +	xchg(&kexec_crash_image, image);
> +}
> +#endif /* CONFIG_CRASH_HOTPLUG */
> +
>  #ifdef CONFIG_PPC_64S_HASH_MMU
>  /* Values we need to export to the second kernel via the device tree. */
>  static unsigned long htab_base;
> diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c
> index eeb258002d1e..9dc774548ce4 100644
> --- a/arch/powerpc/kexec/elf_64.c
> +++ b/arch/powerpc/kexec/elf_64.c
> @@ -24,6 +24,67 @@
>  #include <linux/slab.h>
>  #include <linux/types.h>
>  
> +#include <asm/kvm_book3s.h>
> +#include <asm/kvm_ppc.h>
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +
> +/**
> + * get_cpu_node_sz() - Calculate the space needed to store a CPU device type node
> + *                     in FDT. The calculation is done based on the existing CPU
> + *                     node in unflatten device tree. Loop through all the
> + *                     properties of the very first CPU type device node found in
> + *                     unflatten device tree and returns the sum of the property
> + *                     length and property string size of all properties of a CPU
> + *                     node.
> + */

I don't think this is following the indent rules.

> +static int get_cpu_node_sz(void) {
> +	struct device_node *dn = NULL;
> +	struct property *pp;
> +	int cpu_node_size = 0;
> +
> +	dn = of_find_node_by_type(NULL, "cpu");
> +
> +	if (!dn) {
> +		pr_warn("Unable to locate cpu device_type node.\n");
> +		goto out;
> +	}
> +
> +	/* Every node in FDT starts with FDT_BEGIN_NODE and ends with
> +	 * FDT_END_NODE that takes one byte each.
> +	 */
> +	cpu_node_size = 2;
> +
> +	for_each_property_of_node(dn, pp) {
> +		/* For each property add two bytes extra. One for string null
> +		 * character for property name and other for FDT property start
> +		 * tag FDT_PROP.
> +		 */

Coding style request to start with a blank comment line for multiple
comment lines.

> +		cpu_node_size = cpu_node_size + pp->length + strlen(pp->name) + 2;
> +	}
> +
> +out:
> +	return cpu_node_size;
> +}
> +
> +/**
> + * get_crash_fdt_mem_sz() - calcuate mem size for crash kernel FDT
> + * @fdt: pointer to crash kernel FDT
> + *
> + * Calculate the buffer space needed to add more CPU nodes in crash FDT
> + * post capture kenrel load due to CPU hotplug events.
> + */
> +static unsigned int get_crash_fdt_mem_sz(void *fdt)
> +{
> +	int fdt_cpu_nodes_sz, offline_cpu_cnt;
> +
> +	offline_cpu_cnt = (num_possible_cpus() - num_present_cpus()) / MAX_SMT_THREADS;
> +	fdt_cpu_nodes_sz = get_cpu_node_sz() * offline_cpu_cnt;
> +
> +	return fdt_totalsize(fdt) + fdt_cpu_nodes_sz;
> +}
> +#endif
> +
>  static void *elf64_load(struct kimage *image, char *kernel_buf,
>  			unsigned long kernel_len, char *initrd,
>  			unsigned long initrd_len, char *cmdline,
> @@ -123,6 +184,19 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
>  	kbuf.buf_align = PAGE_SIZE;
>  	kbuf.top_down = true;
>  	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +	if (image->type == KEXEC_TYPE_CRASH) {
> +		kbuf.memsz = get_crash_fdt_mem_sz(fdt);
> +		fdt_set_totalsize(fdt, kbuf.memsz);
> +		image->arch.fdt_index = image->nr_segments;
> +		image->arch.fdt_index_valid = true;
> +	} else
> +#endif
> +	{
> +		kbuf.memsz = fdt_totalsize(fdt);
> +	}
> +
>  	ret = kexec_add_buffer(&kbuf);
>  	if (ret)
>  		goto out_free_fdt;