On Wed, Dec 17, 2025 at 02:32:37PM +0100, Igor Mammedov wrote:
Date: Wed, 17 Dec 2025 14:32:37 +0100 From: Igor Mammedov <imammedo@redhat.com> Subject: Re: [PATCH v5 03/28] pc: Start with modern CPU hotplug interface by default X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-redhat-linux-gnu)
On Wed, 3 Dec 2025 00:28:10 +0800 Zhao Liu <zhao1.liu@intel.com> wrote:
From: Igor Mammedov <imammedo@redhat.com> ^^^ given you resplit original patch, it's better to replace this with you, keeping my SoB is sufficient
Thank you! Will re-organize these signatures
For compatibility reasons PC/Q35 will start with legacy CPU hotplug interface by default but with new CPU hotplug AML code since 2.7 machine type (in commit 679dd1a957df ("pc: use new CPU hotplug interface since 2.7 machine type")). In that way, legacy firmware that doesn't use QEMU generated ACPI tables was able to continue using legacy CPU hotplug interface.
While later machine types, with firmware supporting QEMU provided ACPI tables, generate new CPU hotplug AML, which will switch to new CPU hotplug interface when guest OS executes its _INI method on ACPI tables loading.
Since 2.6 machine type is now gone, and consider that the legacy BIOS (based on QEMU ACPI prior to v2.7) should be no longer in use, previous compatibility requirements are no longer necessary. So initialize 'modern' hotplug directly from the very beginning for PC/Q35 machines with cpu_hotplug_hw_init(), and drop _INIT method.
Additionally, remove the checks and settings around cpu_hotplug_legacy in cpuhp VMState (for piix4 & ich9), to eliminate the risk of segmentation faults, as gpe_cpu no longer has the opportunity to be initialized. This is safe because all hotplug now start with the modern way, and it's impossible to switch to legacy way at runtime (even the "cpu-hotplug-legacy" properties does not allow it either).
Signed-off-by: Igor Mammedov <imammedo@redhat.com> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
tested ping pong cross version (master vs master+this patch) migration with 10.1 machine type, nothing is broken, hence
Acked-by: Igor Mammedov <imammedo@redhat.com>
Thanks for your test and review! Regards, Zhao