Re: [PATCH v10 5/5] powerpc/kexec: add crash memory hotplug support

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On 23/04/2023 12:52:13, Sourabh Jain wrote:
> Extend PowerPC arch crash hotplug handler to support memory hotplug
> events. Since elfcorehdr is used to exchange the memory info between the
> kernels hence it needs to be recreated to reflect the changes due to
> memory hotplug events.
> 
> The way memory hotplug events are handled on PowerPC and the notifier
> call chain used in generic code to trigger the arch crash handler, the
> process to recreate the elfcorehdr is different for memory add and
> remove case.
> 
> For memory remove case the memory change notifier call chain is
> triggered first and then memblock regions is updated. Whereas for the
> memory hot add case, memblock regions are updated before invoking the
> memory change notifier call chain.
> 
> On PowerPC, memblock regions list is used to prepare the elfcorehdr. In
> case of memory hot remove the memblock regions are updated after the
> arch crash hotplug handler is triggered, hence an additional step is
> taken to ensure that memory ranges used to prepare elfcorehdr do not
> include hot removed memory.
> 
> When memory is hot removed it possible that memory regions count may
> increase. So to accommodate a growing number of memory regions, the
> elfcorehdr kexec segment is built with additional buffer space.
> 
> The changes done here will also work for the kexec_load system call given
> that the kexec tool builds the elfcoredhr with additional space to
> accommodate future memory regions as it is done for kexec_file_load
> system call in the kernel.
> 
> Signed-off-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
> Reviewed-by: Laurent Dufour <laurent.dufour@xxxxxxxxxx>

I don't remember sending a review-by on this patch earlier, do you?

> ---
>  arch/powerpc/include/asm/kexec_ranges.h |  1 +
>  arch/powerpc/kexec/core_64.c            | 77 +++++++++++++++++++++-
>  arch/powerpc/kexec/file_load_64.c       | 36 ++++++++++-
>  arch/powerpc/kexec/ranges.c             | 85 +++++++++++++++++++++++++
>  4 files changed, 195 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/kexec_ranges.h b/arch/powerpc/include/asm/kexec_ranges.h
> index f83866a19e870..802abf580cf0f 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 147ea6288a526..01a764b1c9b07 100644
> --- a/arch/powerpc/kexec/core_64.c
> +++ b/arch/powerpc/kexec/core_64.c
> @@ -19,6 +19,7 @@
>  #include <linux/of.h>
>  #include <linux/libfdt.h>
>  #include <linux/memblock.h>
> +#include <linux/memory.h>
>  
>  #include <asm/page.h>
>  #include <asm/current.h>
> @@ -547,6 +548,76 @@ int update_cpus_node(void *fdt)
>  #undef pr_fmt
>  #define pr_fmt(fmt) "crash hp: " fmt
>  
> +/**
> + * update_crash_elfcorehdr() - Recreate the elfcorehdr and replace it with old
> + *			       elfcorehdr in the kexec segment array.
> + * @image: the active struct kimage
> + * @arg: 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 not yet removed from 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);
> +		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_hotplug_handler() - Handle crash CPU/Memory hotplug events to update the
>   *                                necessary kexec segments based on the hotplug event.
> @@ -554,12 +625,14 @@ int update_cpus_node(void *fdt)
>   * @arg: struct memory_notify handler for memory add/remove case and NULL for CPU case.
>   *
>   * Update FDT segment to include newly added CPU. No action for CPU remove case.
> + * Recreate the elfcorehdr for Memory add/remove case and replace it with old one.
>   */
>  void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>  {
>  	void *fdt, *ptr;
>  	unsigned long mem;
>  	int i, fdt_index = -1;
> +	struct memory_notify *mn;
>  	unsigned int hp_action = image->hp_action;
>  
>  	/*
> @@ -569,9 +642,9 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>  	if (hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>  		return;
>  
> -	/* crash update on memory hotplug events is not supported yet */
>  	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");
> +		mn = (struct memory_notify *) arg;
> +		update_crash_elfcorehdr(image, mn);
>  		return;
>  	}
>  
> diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
> index 3554168687869..db7ba1c8c5e0b 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/drmem.h>
>  #include <asm/firmware.h>
> @@ -707,6 +709,30 @@ static void update_backup_region_phdr(struct kimage *image, Elf64_Ehdr *ehdr)
>  	}
>  }
>  
> +/* get_max_phdr - Find the total number of Phdr needed to represent the
> + *		  max memory in the kdump elfcorehdr.
> + *
> + * @cmem: crash memory ranges in the system.
> + */
> +static int get_max_phdr(struct crash_mem *cmem)
> +{
> +	int max_lmb;
> +
> +	/* 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)
> +		return PN_XNUM - cmem->nr_ranges;
> +
> +	return max_lmb - cmem->nr_ranges;
> +}
> +
>  /**
>   * load_elfcorehdr_segment - Setup crash memory ranges and initialize elfcorehdr
>   *                           segment needed to load kdump kernel.
> @@ -738,7 +764,13 @@ 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;
> +/* Additional buffer space to accommodate future memory ranges */
> +#if defined(CONFIG_MEMORY_HOTPLUG)
> +	kbuf->memsz = headers_sz + get_max_phdr(cmem) * sizeof(Elf64_Phdr);
> +#else
> +	kbuf->memsz = headers_sz;
> +#endif
>  	kbuf->top_down = false;
>  
>  	ret = kexec_add_buffer(kbuf);
> @@ -748,7 +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 5fc53a5fcfdf6..d8007363cdc11 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.


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