Re: [edk2-devel] [PATCH v3 0/2] OvmfPkg/PlatformInitLib: catch QEMU's CPU hotplug reg block regression

["Michael Brown" <mcb30@ipxe.org>]

On 19/01/2023 11:01, Laszlo Ersek wrote:
>> PlatformCpuCountBugCheck: Present=0 Possible=1
>> PlatformCpuCountBugCheck: Broken CPU hotplug register block found. Update QEMU to version 8+, or
>> PlatformCpuCountBugCheck: to a stable release with commit dab30fbef389 backported. Refer to
>> PlatformCpuCountBugCheck: <https://bugzilla.tianocore.org/show_bug.cgi?id=4250>.
>> PlatformCpuCountBugCheck: Consequences of the QEMU bug may include, but are not limited to:
>> PlatformCpuCountBugCheck: - all firmware logic, dependent on the CPU hotplug register block,
>> PlatformCpuCountBugCheck:   being confused, for example, multiprocessing-related logic;
>> PlatformCpuCountBugCheck: - guest OS data loss, including filesystem corruption, due to crash or
>> PlatformCpuCountBugCheck:   hang during ACPI S3 resume;
>> PlatformCpuCountBugCheck: - SMM privilege escalation, by a malicious guest OS or 3rd partty UEFI
>> PlatformCpuCountBugCheck:   agent, against the platform firmware.
>> PlatformCpuCountBugCheck: These symptoms need not necessarily be limited to the QEMU user
>> PlatformCpuCountBugCheck: attempting to hot(un)plug a CPU.
>> PlatformCpuCountBugCheck: The firmware will now stop (hang) deliberately, in order to prevent the
>> PlatformCpuCountBugCheck: above symptoms.
>> PlatformCpuCountBugCheck: You can forcibly override the hang, *at your own risk*, with the
>> PlatformCpuCountBugCheck: following *experimental* QEMU command line option:
>> PlatformCpuCountBugCheck:   -fw_cfg name=opt/org.tianocore/X-Cpuhp-Bugcheck-Override,string=yes
>> PlatformCpuCountBugCheck: Please only report such bugs that you can reproduce *without* the
>> PlatformCpuCountBugCheck: override.

Laszlo: thank you for taking the time to deal with this so thoroughly 
and to see it through to its conclusion.

For what it's worth:

Hugely-appreciated-by: Michael Brown <mcb30@ipxe.org>

Thanks,

Michael