[PATCH v17 6/6] powerpc/crash: add crash memory hotplug support
Hari Bathini
hbathini at linux.ibm.com
Sat Mar 2 05:19:55 PST 2024
On 26/02/24 2:11 pm, Sourabh Jain wrote:
> Extend the arch crash hotplug handler, as introduced by the patch title
> ("powerpc: add crash CPU hotplug support"), to also support memory
> add/remove events.
>
> Elfcorehdr describes the memory of the crash kernel to capture the
> kernel; hence, it needs to be updated if memory resources change due to
> memory add/remove events. Therefore, arch_crash_handle_hotplug_event()
> is updated to recreate the elfcorehdr and replace it with the previous
> one on memory add/remove events.
>
> The memblock list is used to prepare the elfcorehdr. In the case of
> memory hot remove, the memblock list is updated after the arch crash
> hotplug handler is triggered, as depicted in Figure 1. Thus, the
> hot-removed memory is explicitly removed from the crash memory ranges
> to ensure that the memory ranges added to elfcorehdr do not include the
> hot-removed memory.
>
> Memory remove
> |
> v
> Offline pages
> |
> v
> Initiate memory notify call <----> crash hotplug handler
> chain for MEM_OFFLINE event
> |
> v
> Update memblock list
>
> Figure 1
>
> There are two system calls, `kexec_file_load` and `kexec_load`, used to
> load the kdump image. A few changes have been made to ensure that the
> kernel can safely update the elfcorehdr component of the kdump image for
> both system calls.
>
> For the kexec_file_load syscall, kdump image is prepared in the kernel.
> To support an increasing number of memory regions, the elfcorehdr is
> built with extra buffer space to ensure that it can accommodate
> additional memory ranges in future.
>
> For the kexec_load syscall, the elfcorehdr is updated only if the
> KEXEC_CRASH_HOTPLUG_SUPPORT kexec flag is passed to the kernel by the
> kexec tool. Passing this flag to the kernel indicates that the
> elfcorehdr is built to accommodate additional memory ranges and the
> elfcorehdr segment is not considered for SHA calculation, making it safe
> to update.
>
> The changes related to this feature are kept under the CRASH_HOTPLUG
> config, and it is enabled by default.
>
Overall, the patchset looks good. I tried out the changes too.
Acked-by: Hari Bathini <hbathini at linux.ibm.com>
> Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
> Cc: Akhil Raj <lf32.dev at gmail.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Aneesh Kumar K.V <aneesh.kumar at kernel.org>
> Cc: Baoquan He <bhe at redhat.com>
> Cc: Borislav Petkov (AMD) <bp at alien8.de>
> Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> Cc: Dave Hansen <dave.hansen at linux.intel.com>
> Cc: Dave Young <dyoung at redhat.com>
> Cc: David Hildenbrand <david at redhat.com>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Cc: Hari Bathini <hbathini at linux.ibm.com>
> Cc: Laurent Dufour <laurent.dufour at fr.ibm.com>
> Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Mimi Zohar <zohar at linux.ibm.com>
> Cc: Naveen N Rao <naveen at kernel.org>
> Cc: Oscar Salvador <osalvador at suse.de>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Valentin Schneider <vschneid at redhat.com>
> Cc: Vivek Goyal <vgoyal at redhat.com>
> Cc: kexec at lists.infradead.org
> Cc: x86 at kernel.org
> ---
> arch/powerpc/include/asm/kexec.h | 3 +
> arch/powerpc/include/asm/kexec_ranges.h | 1 +
> arch/powerpc/kexec/crash.c | 95 ++++++++++++++++++++++++-
> arch/powerpc/kexec/file_load_64.c | 20 +++++-
> arch/powerpc/kexec/ranges.c | 85 ++++++++++++++++++++++
> 5 files changed, 202 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h
> index e75970351bcd..95a98b390d62 100644
> --- a/arch/powerpc/include/asm/kexec.h
> +++ b/arch/powerpc/include/asm/kexec.h
> @@ -141,6 +141,9 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg);
>
> int arch_crash_hotplug_support(struct kimage *image, unsigned long kexec_flags);
> #define arch_crash_hotplug_support arch_crash_hotplug_support
> +
> +unsigned int arch_crash_get_elfcorehdr_size(void);
> +#define crash_get_elfcorehdr_size arch_crash_get_elfcorehdr_size
> #endif /* CONFIG_CRASH_HOTPLUG */
>
> extern int crashing_cpu;
> diff --git a/arch/powerpc/include/asm/kexec_ranges.h b/arch/powerpc/include/asm/kexec_ranges.h
> index 8489e844b447..14055896cbcb 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 get_exclude_memory_ranges(struct crash_mem **mem_ranges);
> int get_reserved_memory_ranges(struct crash_mem **mem_ranges);
> int get_crash_memory_ranges(struct crash_mem **mem_ranges);
> diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
> index 8938a19af12f..21b193e938a3 100644
> --- a/arch/powerpc/kexec/crash.c
> +++ b/arch/powerpc/kexec/crash.c
> @@ -17,6 +17,7 @@
> #include <linux/irq.h>
> #include <linux/types.h>
> #include <linux/libfdt.h>
> +#include <linux/memory.h>
>
> #include <asm/processor.h>
> #include <asm/machdep.h>
> @@ -25,6 +26,7 @@
> #include <asm/setjmp.h>
> #include <asm/debug.h>
> #include <asm/interrupt.h>
> +#include <asm/kexec_ranges.h>
>
> /*
> * The primary CPU waits a while for all secondary CPUs to enter. This is to
> @@ -398,6 +400,94 @@ void default_machine_crash_shutdown(struct pt_regs *regs)
> #undef pr_fmt
> #define pr_fmt(fmt) "crash hp: " fmt
>
> +/*
> + * Advertise preferred elfcorehdr size to userspace via
> + * /sys/kernel/crash_elfcorehdr_size sysfs interface.
> + */
> +unsigned int arch_crash_get_elfcorehdr_size(void)
> +{
> + unsigned long phdr_cnt;
> +
> + /* A program header for possible CPUs + vmcoreinfo */
> + phdr_cnt = num_possible_cpus() + 1;
> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> + phdr_cnt += CONFIG_CRASH_MAX_MEMORY_RANGES;
> +
> + return sizeof(struct elfhdr) + (phdr_cnt * sizeof(Elf64_Phdr));
> +}
> +
> +/**
> + * 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);
> + if (ret) {
> + pr_err("Failed to remove hot-unplugged memory from crash memory ranges\n");
> + goto out;
> + }
> + }
> +
> + ret = crash_prepare_elf64_headers(cmem, false, &elfbuf, &elfsz);
> + if (ret) {
> + pr_err("Failed to prepare elf header\n");
> + goto out;
> + }
> +
> + /*
> + * 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:
> + kvfree(cmem);
> + if (elfbuf)
> + kvfree(elfbuf);
> +}
> +
> /**
> * get_fdt_index - Loop through the kexec segment array and find
> * the index of the FDT segment.
> @@ -478,6 +568,8 @@ int arch_crash_hotplug_support(struct kimage *image, unsigned long kexec_flags)
> */
> void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
> {
> + struct memory_notify *mn;
> +
> switch (image->hp_action) {
> case KEXEC_CRASH_HP_REMOVE_CPU:
> return;
> @@ -488,7 +580,8 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>
> case KEXEC_CRASH_HP_REMOVE_MEMORY:
> case 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;
> default:
> pr_warn_once("Unknown hotplug action\n");
> diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
> index 2640a804fcdf..925a69ad2468 100644
> --- a/arch/powerpc/kexec/file_load_64.c
> +++ b/arch/powerpc/kexec/file_load_64.c
> @@ -595,6 +595,23 @@ static void update_backup_region_phdr(struct kimage *image, Elf64_Ehdr *ehdr)
> }
> }
>
> +static unsigned int kdump_extra_elfcorehdr_size(struct crash_mem *cmem)
> +{
> +#if defined(CONFIG_CRASH_HOTPLUG) && defined(CONFIG_MEMORY_HOTPLUG)
> + unsigned int extra_sz = 0;
> +
> + if (CONFIG_CRASH_MAX_MEMORY_RANGES > (unsigned int)PN_XNUM)
> + pr_warn("Number of Phdrs %u exceeds max\n", CONFIG_CRASH_MAX_MEMORY_RANGES);
> + else if (cmem->nr_ranges >= CONFIG_CRASH_MAX_MEMORY_RANGES)
> + pr_warn("Configured crash mem ranges may not be enough\n");
> + else
> + extra_sz = (CONFIG_CRASH_MAX_MEMORY_RANGES - cmem->nr_ranges) * sizeof(Elf64_Phdr);
> +
> + return extra_sz;
> +#endif
> + return 0;
> +}
> +
> /**
> * load_elfcorehdr_segment - Setup crash memory ranges and initialize elfcorehdr
> * segment needed to load kdump kernel.
> @@ -626,7 +643,8 @@ 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;
> + kbuf->memsz = headers_sz + kdump_extra_elfcorehdr_size(cmem);
> kbuf->top_down = false;
>
> ret = kexec_add_buffer(kbuf);
> diff --git a/arch/powerpc/kexec/ranges.c b/arch/powerpc/kexec/ranges.c
> index 297b8bc97b9f..00dfd62203bd 100644
> --- a/arch/powerpc/kexec/ranges.c
> +++ b/arch/powerpc/kexec/ranges.c
> @@ -618,4 +618,89 @@ int get_crash_memory_ranges(struct crash_mem **mem_ranges)
> pr_err("Failed to setup crash memory ranges\n");
> return ret;
> }
> +
> +/**
> + * 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;
> +}
> #endif /* CONFIG_CRASH_DUMP */
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