Re: [PATCH v14 6/6] powerpc: add crash memory hotplug support

[Baoquan He <bhe@redhat.com>]

On 12/11/23 at 02:00pm, Sourabh Jain wrote:
...... 
> diff --git a/arch/powerpc/include/asm/kexec_ranges.h b/arch/powerpc/include/asm/kexec_ranges.h
> index f83866a19e87..802abf580cf0 100644
> --- a/arch/powerpc/include/asm/kexec_ranges.h
> +++ b/arch/powerpc/include/asm/kexec_ranges.h
> @@ -7,6 +7,7 @@
>  void sort_memory_ranges(struct crash_mem *mrngs, bool merge);
>  struct crash_mem *realloc_mem_ranges(struct crash_mem **mem_ranges);
>  int add_mem_range(struct crash_mem **mem_ranges, u64 base, u64 size);
> +int remove_mem_range(struct crash_mem **mem_ranges, u64 base, u64 size);
>  int add_tce_mem_ranges(struct crash_mem **mem_ranges);
>  int add_initrd_mem_range(struct crash_mem **mem_ranges);
>  #ifdef CONFIG_PPC_64S_HASH_MMU
> diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c
> index 9932793cd64b..5be30659172f 100644
> --- a/arch/powerpc/kexec/core_64.c
> +++ b/arch/powerpc/kexec/core_64.c
> @@ -19,8 +19,11 @@
>  #include <linux/of.h>
>  #include <linux/libfdt.h>
>  #include <linux/memblock.h>
> +#include <linux/memory.h>
>  
>  #include <asm/page.h>
> +#include <asm/drmem.h>
> +#include <asm/mmzone.h>
>  #include <asm/current.h>
>  #include <asm/machdep.h>
>  #include <asm/cacheflush.h>
> @@ -547,9 +550,7 @@ int update_cpus_node(void *fdt)
>  #undef pr_fmt
>  #define pr_fmt(fmt) "crash hp: " fmt
>  
> -#ifdef CONFIG_HOTPLUG_CPU
> - /* Provides the value for the sysfs crash_hotplug nodes */
> -int arch_crash_hotplug_cpu_support(struct kimage *image)
> +static int crash_hotplug_support(struct kimage *image)
>  {
>  	if (image->file_mode)
>  		return 1;
> @@ -560,8 +561,118 @@ int arch_crash_hotplug_cpu_support(struct kimage *image)
>  	 */
>  	return image->update_elfcorehdr && image->update_fdt;
>  }
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> + /* Provides the value for the sysfs crash_hotplug nodes */
> +int arch_crash_hotplug_cpu_support(struct kimage *image)
> +{
> +	return crash_hotplug_support(image);
> +}
> +#endif
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> + /* Provides the value for the sysfs memory_hotplug nodes */
> +int arch_crash_hotplug_memory_support(struct kimage *image)
> +{
> +	return crash_hotplug_support(image);
> +}
>  #endif
>  
> +/*
> + * Advertise preferred elfcorehdr size to userspace via
> + * /sys/kernel/crash_elfcorehdr_size sysfs interface.
> + */
> +unsigned int arch_crash_get_elfcorehdr_size(void)
> +{
> +	unsigned int sz;
> +	unsigned long elf_phdr_cnt;
> +
> +	/* Program header for CPU notes and vmcoreinfo */
> +	elf_phdr_cnt = 2;
> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> +		/* In the worst case, a Phdr is needed for every other LMB to be
> +		 * represented as an individual crash range.
> +		 */
> +		elf_phdr_cnt += memory_hotplug_max() / (2 * drmem_lmb_size());
> +
> +	/* Do not cross the max limit */
> +	if (elf_phdr_cnt > PN_XNUM)
> +		elf_phdr_cnt = PN_XNUM;
> +
> +	sz = sizeof(struct elfhdr) + (elf_phdr_cnt * sizeof(Elf64_Phdr));
> +	return sz;
> +}
> +
> +/**
> + * update_crash_elfcorehdr() - Recreate the elfcorehdr and replace it with old
> + *			       elfcorehdr in the kexec segment array.
> + * @image: the active struct kimage
> + * @mn: struct memory_notify data handler
> + */
> +static void update_crash_elfcorehdr(struct kimage *image, struct memory_notify *mn)
> +{
> +	int ret;
> +	struct crash_mem *cmem = NULL;
> +	struct kexec_segment *ksegment;
> +	void *ptr, *mem, *elfbuf = NULL;
> +	unsigned long elfsz, memsz, base_addr, size;
> +
> +	ksegment = &image->segment[image->elfcorehdr_index];
> +	mem = (void *) ksegment->mem;
> +	memsz = ksegment->memsz;
> +
> +	ret = get_crash_memory_ranges(&cmem);
> +	if (ret) {
> +		pr_err("Failed to get crash mem range\n");
> +		return;
> +	}
> +
> +	/*
> +	 * The hot unplugged memory is part of crash memory ranges,
> +	 * remove it here.
> +	 */
> +	if (image->hp_action == KEXEC_CRASH_HP_REMOVE_MEMORY) {
> +		base_addr = PFN_PHYS(mn->start_pfn);
> +		size = mn->nr_pages * PAGE_SIZE;
> +		ret = remove_mem_range(&cmem, base_addr, size);

Althouth this is ppc specific, I don't understand. Why don't you
recreate the elfcorehdr, but take removing the removed region. Comparing the
remove_mem_range() implementation with recreating, I don't see too much
benefit from that, and it makes your code more complicated. Just
curious, surely ppc people can decide what should be taken. 

> +		if (ret) {
> +			pr_err("Failed to remove hot-unplugged from crash memory ranges.\n");
> +			return;
> +		}
> +	}
> +
> +	ret = crash_prepare_elf64_headers(cmem, false, &elfbuf, &elfsz);
> +	if (ret) {
> +		pr_err("Failed to prepare elf header\n");
> +		return;
> +	}
> +
> +	/*
> +	 * It is unlikely that kernel hit this because elfcorehdr kexec
> +	 * segment (memsz) is built with addition space to accommodate growing
> +	 * number of crash memory ranges while loading the kdump kernel. It is
> +	 * Just to avoid any unforeseen case.
> +	 */
> +	if (elfsz > memsz) {
> +		pr_err("Updated crash elfcorehdr elfsz %lu > memsz %lu", elfsz, memsz);
> +		goto out;
> +	}
> +
> +	ptr = __va(mem);
> +	if (ptr) {
> +		/* Temporarily invalidate the crash image while it is replaced */
> +		xchg(&kexec_crash_image, NULL);
> +
> +		/* Replace the old elfcorehdr with newly prepared elfcorehdr */
> +		memcpy((void *)ptr, elfbuf, elfsz);
> +
> +		/* The crash image is now valid once again */
> +		xchg(&kexec_crash_image, image);
> +	}
> +out:
> +	vfree(elfbuf);
> +}
> +
>  /**
>   * arch_crash_handle_hotplug_event - Handle crash CPU/Memory hotplug events to update the
>   *				     necessary kexec segments based on the hotplug event.
> @@ -572,7 +683,7 @@ int arch_crash_hotplug_cpu_support(struct kimage *image)
>   * CPU addition: Update the FDT segment to include the newly added CPU.
>   * CPU removal: No action is needed, with the assumption that it's okay to have offline CPUs
>   *		as part of the FDT.
> - * Memory addition/removal: No action is taken as this is not yet supported.
> + * Memory addition/removal: Recreate the elfcorehdr segment
>   */
>  void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>  {
> @@ -593,7 +704,6 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>  		return;
>  
>  	} else if (hp_action == KEXEC_CRASH_HP_ADD_CPU) {
> -
>  		void *fdt, *ptr;
>  		unsigned long mem;
>  		int i, fdt_index = -1;
> @@ -628,8 +738,10 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>  
>  	} else if (hp_action == KEXEC_CRASH_HP_REMOVE_MEMORY ||
>  		   hp_action == KEXEC_CRASH_HP_ADD_MEMORY) {
> -		pr_info_once("Crash update is not supported for memory hotplug\n");
> -		return;
> +		struct memory_notify *mn;
> +
> +		mn = (struct memory_notify *)arg;
> +		update_crash_elfcorehdr(image, mn);
>  	}
>  }
>  #endif
> diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
> index e2148a009701..2457d7ec2075 100644
> --- a/arch/powerpc/kexec/file_load_64.c
> +++ b/arch/powerpc/kexec/file_load_64.c
> @@ -21,6 +21,8 @@
>  #include <linux/memblock.h>
>  #include <linux/slab.h>
>  #include <linux/vmalloc.h>
> +#include <linux/elf.h>
> +
>  #include <asm/setup.h>
>  #include <asm/cputhreads.h>
>  #include <asm/drmem.h>
> @@ -740,7 +742,35 @@ static int load_elfcorehdr_segment(struct kimage *image, struct kexec_buf *kbuf)
>  
>  	kbuf->buffer = headers;
>  	kbuf->mem = KEXEC_BUF_MEM_UNKNOWN;
> -	kbuf->bufsz = kbuf->memsz = headers_sz;
> +	kbuf->bufsz = headers_sz;
> +#if defined(CONFIG_CRASH_HOTPLUG) && defined(CONFIG_MEMORY_HOTPLUG)
> +	/* Adjust the elfcorehdr segment size to accommodate
> +	 * future crash memory ranges.
> +	 */
> +	int max_lmb;
> +	unsigned long pnum;
> +
> +	/* In the worst case, a Phdr is needed for every other LMB to be
> +	 * represented as an individual crash range.
> +	 */
> +	max_lmb = memory_hotplug_max() / (2 * drmem_lmb_size());
> +
> +	/* Do not cross the Phdr max limit of the elf header.
> +	 * Avoid counting Phdr for crash ranges (cmem->nr_ranges)
> +	 * which are already part of elfcorehdr.
> +	 */
> +	if (max_lmb > PN_XNUM)
> +		pnum = PN_XNUM - cmem->nr_ranges;
> +	else
> +		pnum = max_lmb - cmem->nr_ranges;
> +
> +	/* Additional buffer space for elfcorehdr to accommodate
> +	 * future memory ranges.
> +	 */
> +	kbuf->memsz = headers_sz + pnum * sizeof(Elf64_Phdr);
> +#else
> +	kbuf->memsz = headers_sz;
> +#endif
>  	kbuf->top_down = false;
>  
>  	ret = kexec_add_buffer(kbuf);
> @@ -750,7 +780,7 @@ static int load_elfcorehdr_segment(struct kimage *image, struct kexec_buf *kbuf)
>  	}
>  
>  	image->elf_load_addr = kbuf->mem;
> -	image->elf_headers_sz = headers_sz;
> +	image->elf_headers_sz = kbuf->memsz;
>  	image->elf_headers = headers;
>  out:
>  	kfree(cmem);
> diff --git a/arch/powerpc/kexec/ranges.c b/arch/powerpc/kexec/ranges.c
> index fb3e12f15214..4fd0c5d5607b 100644
> --- a/arch/powerpc/kexec/ranges.c
> +++ b/arch/powerpc/kexec/ranges.c
> @@ -234,6 +234,91 @@ int add_mem_range(struct crash_mem **mem_ranges, u64 base, u64 size)
>  	return __add_mem_range(mem_ranges, base, size);
>  }
>  
> +/**
> + * remove_mem_range - Removes the given memory range from the range list.
> + * @mem_ranges:    Range list to remove the memory range to.
> + * @base:          Base address of the range to remove.
> + * @size:          Size of the memory range to remove.
> + *
> + * (Re)allocates memory, if needed.
> + *
> + * Returns 0 on success, negative errno on error.
> + */
> +int remove_mem_range(struct crash_mem **mem_ranges, u64 base, u64 size)
> +{
> +	u64 end;
> +	int ret = 0;
> +	unsigned int i;
> +	u64 mstart, mend;
> +	struct crash_mem *mem_rngs = *mem_ranges;
> +
> +	if (!size)
> +		return 0;
> +
> +	/*
> +	 * Memory range are stored as start and end address, use
> +	 * the same format to do remove operation.
> +	 */
> +	end = base + size - 1;
> +
> +	for (i = 0; i < mem_rngs->nr_ranges; i++) {
> +		mstart = mem_rngs->ranges[i].start;
> +		mend = mem_rngs->ranges[i].end;
> +
> +		/*
> +		 * Memory range to remove is not part of this range entry
> +		 * in the memory range list
> +		 */
> +		if (!(base >= mstart && end <= mend))
> +			continue;
> +
> +		/*
> +		 * Memory range to remove is equivalent to this entry in the
> +		 * memory range list. Remove the range entry from the list.
> +		 */
> +		if (base == mstart && end == mend) {
> +			for (; i < mem_rngs->nr_ranges - 1; i++) {
> +				mem_rngs->ranges[i].start = mem_rngs->ranges[i+1].start;
> +				mem_rngs->ranges[i].end = mem_rngs->ranges[i+1].end;
> +			}
> +			mem_rngs->nr_ranges--;
> +			goto out;
> +		}
> +		/*
> +		 * Start address of the memory range to remove and the
> +		 * current memory range entry in the list is same. Just
> +		 * move the start address of the current memory range
> +		 * entry in the list to end + 1.
> +		 */
> +		else if (base == mstart) {
> +			mem_rngs->ranges[i].start = end + 1;
> +			goto out;
> +		}
> +		/*
> +		 * End address of the memory range to remove and the
> +		 * current memory range entry in the list is same.
> +		 * Just move the end address of the current memory
> +		 * range entry in the list to base - 1.
> +		 */
> +		else if (end == mend)  {
> +			mem_rngs->ranges[i].end = base - 1;
> +			goto out;
> +		}
> +		/*
> +		 * Memory range to remove is not at the edge of current
> +		 * memory range entry. Split the current memory entry into
> +		 * two half.
> +		 */
> +		else {
> +			mem_rngs->ranges[i].end = base - 1;
> +			size = mem_rngs->ranges[i].end - end;
> +			ret = add_mem_range(mem_ranges, end + 1, size);
> +		}
> +	}
> +out:
> +	return ret;
> +}
> +
>  /**
>   * add_tce_mem_ranges - Adds tce-table range to the given memory ranges list.
>   * @mem_ranges:         Range list to add the memory range(s) to.
> -- 
> 2.41.0
> 


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