A VMware guest may have no persistent storage or working userspace after a crash. Preserve its newest kernel log tail in the host's vmware.log before entering kdump, without enabling every panic notifier by default.
Following Petr's suggestion, add one generic panic_pre_kdump_list with VMware as its first client. A set-once helper covers panic() and direct crash-kexec entry. Fatal oopses can reach kdump without calling panic(), so patch 2 adds that call after capturing the original registers under the existing kexec lock. The late panic call follows sys_info() and precedes the kmsg dumpers. Patch 3 adds Guilherme's suggested escape hatch for debugging kdump failures involving early callbacks. With panic_pre_kdump_postpone set, the list runs before kdump only when crash_kexec_post_notifiers is also set. This can omit hypervisor crash handling as well as diagnostics. The late panic call remains eligible. This policy is a separate patch; I can omit patch 3 if it is not wanted. The logger preallocates an 8 KiB buffer and bounds its register-based RPC transfer and retries. Michael suggested increasing the buffer because 4 KiB can omit useful stack-trace context. Ordinary guests enable logging by default; encrypted guests must opt in. Use bool/proc_dobool for the sysctl as Joel requested. The potentially terminating REPORTGUESTCRASH event remains a separate late dumper, suppressed whenever a crash image is loaded. The v1 assignment to crash_kexec_post_notifiers is dropped. Tested on VMware Workstation and ESXi with ordinary guests, and on ESXi with SEV-SNP and TDX guests. v1: https://lore.kernel.org/r/[email protected] Zack Rusin (6): panic: Add a notifier chain for pre-kdump callbacks crash: Notify pre-kdump callbacks before switching kernels panic: Allow postponing pre-kdump notifiers x86/vmware: Add a bounded pre-kdump log sender x86/vmware: Add the vmware_record_panic_msg sysctl x86/vmware: Report guest crashes after kmsg dumpers .../admin-guide/kernel-parameters.txt | 14 + Documentation/admin-guide/sysctl/kernel.rst | 20 ++ arch/x86/include/asm/vmware.h | 2 + arch/x86/kernel/cpu/vmware.c | 250 ++++++++++++++++++ include/linux/panic_notifier.h | 4 + kernel/crash_core.c | 3 + kernel/panic.c | 28 ++ 7 files changed, 321 insertions(+) base-commit: fd73f4a6659897191fa0d40695fe370925dd3780
