Re: [PATCH v2 0/6] panic, x86/vmware: Preserve crash logs before kdump
From: Bradley Morgan
Date: Mon Sep 28 2026 - 16:40:55 EST
On 28 September 2026 18:55:34 BST, Zack Rusin <zack.rusin@xxxxxxxxxxxx>
wrote:
>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/cover.1788414671.git.zack.rusin@xxxxxxxxxxxx
>
>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(+)
>
All the panic changes and crash_core changes looks good to me!
Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
Tested basic panic calls with Power10, in courtesy of osuosl:
Tested-by: Bradley Morgan <brads@xxxxxxxxxxxxxx> # Power10
>
>base-commit: fd73f4a6659897191fa0d40695fe370925dd3780
>
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>From: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
>To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>,
> Petr Mladek <pmladek@xxxxxxxx>,
> Baoquan He <baoquan.he@xxxxxxxxx>,
> Mike Rapoport <rppt@xxxxxxxxxx>,
> Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>,
> Pratyush Yadav <pratyush@xxxxxxxxxx>,
> Dave Young <ruirui.yang@xxxxxxxxx>
>Cc: Borislav Petkov <bp@xxxxxxxxx>,
> Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>,
> Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>,
> x86@xxxxxxxxxx,
> Joel Granados <joel.granados@xxxxxxxxxx>,
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> "H. Peter Anvin" <hpa@xxxxxxxxx>,
> virtualization@xxxxxxxxxxxxxxx,
> bcm-kernel-feedback-list@xxxxxxxxxxxx,
> linux-kernel@xxxxxxxxxxxxxxx,
> John Ogness <john.ogness@xxxxxxxxxxxxx>,
> Steven Rostedt <rostedt@xxxxxxxxxxx>,
> Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>,
> Kees Cook <kees@xxxxxxxxxx>,
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> kexec@xxxxxxxxxxxxxxxxxxx,
> linux-doc@xxxxxxxxxxxxxxx,
> "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>,
> Maaz Mombasawala <maaz.mombasawala@xxxxxxxxxxxx>,
> Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>,
> Randy Dunlap <rdunlap@xxxxxxxxxxxxx>,
> Stephen Brennan <stephen.s.brennan@xxxxxxxxxx>,
> Michael Kelley <mhklinux@xxxxxxxxxxx>,
> Ian Forbes <ian.forbes@xxxxxxxxxxxx>
>Subject: [PATCH v2 0/6] panic, x86/vmware: Preserve crash logs before kdump
>Date: Mon, 28 Sep 2026 13:55:34 -0400
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>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/cover.1788414671.git.zack.rusin@xxxxxxxxxxxx
>
>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
>
>
--- Thanks!
"I'm not a very positive person" - Linus torvalds