A virtual machine may have neither guest-local persistent storage nor
working userspace after a panic. The host's vmware.log remains available
after the VM terminates, and a production encrypted guest is the only
component able to export readable panic text. Hyper-V already provides
this class of host-persistent panic reporting.

Add a panic-only VMware logger that copies the newest 4 KiB of the kernel
log and sends it with bounded low-bandwidth RPC work. Ordinary guests
enable text transfer by default; encrypted guests require an administrator
to opt in through kernel.vmware_record_panic_msg. A separate late dumper
reports the structured crash event after built-in dumpers and suppresses
the event while a crash kernel is loaded, because a configured VMware host
may terminate the VM before the reporting hypercall returns.

Patch 4 makes panic diagnostics run before kdump by default on VMware
guests. This follows existing platform uses of
crash_kexec_post_notifiers, with Hyper-V as the closest guest-reporting
precedent. Unlike Hyper-V, VMware exposes no capability bit for this
behavior. An explicit crash_kexec_post_notifiers=0 still wins, and patch 4
can be dropped without affecting patches 1 through 3.

This replaces patches 2 and 3 of Alexey's v2 posting:
https://lore.kernel.org/all/20260309235250.2611115-1-alexey.makhalov@broadcom.com/

The intended merge path is tip's x86/vmware branch. Boris please review the
VMware transport and policy. Petr and John, please review the panic-only
dumper use and registration ordering. Joel and Kees, please review the
sysctl. Baoquan and the KEXEC/KDUMP team, please review the 
loaded-crash-kernel guard and the default in patch 4.

Zack Rusin (4):
  x86/vmware: Add a bounded panic log sender
  x86/vmware: Add the vmware_record_panic_msg sysctl
  x86/vmware: Report guest crashes after kmsg dumpers
  x86/vmware: Run panic diagnostics before kdump by default

 Documentation/admin-guide/sysctl/kernel.rst |  14 ++
 arch/x86/include/asm/vmware.h               |   2 +
 arch/x86/kernel/cpu/vmware.c                | 245 ++++++++++++++++++++
 3 files changed, 261 insertions(+)


base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.53.0

On 9/8/26 11:07 AM, Zack Rusin wrote:
> A virtual machine may have neither guest-local persistent storage nor
> working userspace after a panic. The host's vmware.log remains available
> after the VM terminates, and a production encrypted guest is the only
> component able to export readable panic text. Hyper-V already provides
> this class of host-persistent panic reporting.
> 
> Add a panic-only VMware logger that copies the newest 4 KiB of the kernel
> log and sends it with bounded low-bandwidth RPC work. Ordinary guests
> enable text transfer by default; encrypted guests require an administrator
> to opt in through kernel.vmware_record_panic_msg. A separate late dumper
> reports the structured crash event after built-in dumpers and suppresses
> the event while a crash kernel is loaded, because a configured VMware host
> may terminate the VM before the reporting hypercall returns.
> 
> Patch 4 makes panic diagnostics run before kdump by default on VMware
> guests. This follows existing platform uses of
> crash_kexec_post_notifiers, with Hyper-V as the closest guest-reporting
> precedent. Unlike Hyper-V, VMware exposes no capability bit for this
> behavior. An explicit crash_kexec_post_notifiers=0 still wins, and patch 4
> can be dropped without affecting patches 1 through 3.
> 
> This replaces patches 2 and 3 of Alexey's v2 posting:
> https://lore.kernel.org/all/20260309235250.2611115-1-alexey.makhalov@broadcom.com/
> 
> The intended merge path is tip's x86/vmware branch. Boris please review the
> VMware transport and policy. Petr and John, please review the panic-only
> dumper use and registration ordering. Joel and Kees, please review the
> sysctl. Baoquan and the KEXEC/KDUMP team, please review the 
> loaded-crash-kernel guard and the default in patch 4.
> 
> Zack Rusin (4):
>   x86/vmware: Add a bounded panic log sender
>   x86/vmware: Add the vmware_record_panic_msg sysctl
>   x86/vmware: Report guest crashes after kmsg dumpers
>   x86/vmware: Run panic diagnostics before kdump by default
> 
>  Documentation/admin-guide/sysctl/kernel.rst |  14 ++
>  arch/x86/include/asm/vmware.h               |   2 +
>  arch/x86/kernel/cpu/vmware.c                | 245 ++++++++++++++++++++
>  3 files changed, 261 insertions(+)
> 
> 
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935


LGTM for the series

Reviewed-by: Maaz Mombasawala <maaz.mombasawala@broadcom.com>

-- 
Maaz Mombasawala <maaz.mombasawala@broadcom.com>