[PATCH v10 5/5] powerpc/kexec: add crash memory hotplug support
Laurent Dufour
ldufour at linux.ibm.com
Mon Apr 24 20:00:00 AEST 2023
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 at linux.ibm.com>
> Reviewed-by: Laurent Dufour <laurent.dufour at fr.ibm.com>
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.
More information about the Linuxppc-dev
mailing list