Hotpluggable CPUs MUST be exposed as 'online-capable' according to the new change. However, cold-booted CPUs, if marked as 'online-capable' during boot time, might not be detected by legacy operating systems. This could cause compatibility problems.
Original Change Link: https://bugzilla.tianocore.org/show_bug.cgi?id=3706 Since updating the specification might take time, it is necessary to disable the support for unplugging any cold-booted CPUs to preserve compatibility with legacy operating systems. Signed-off-by: Salil Mehta <salil.me...@huawei.com> --- hw/arm/virt-acpi-build.c | 29 ++++++++++++++++++++--------- hw/arm/virt.c | 16 ++++++++++++++++ include/hw/core/cpu.h | 2 ++ 3 files changed, 38 insertions(+), 9 deletions(-) diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c index 6cb613103f..322ed8e35b 100644 --- a/hw/arm/virt-acpi-build.c +++ b/hw/arm/virt-acpi-build.c @@ -667,17 +667,28 @@ static uint32_t virt_acpi_get_gicc_flags(CPUState *cpu) } /* - * ARM GIC CPU Interface can be 'online-capable' or 'enabled' at boot - * We MUST set 'online-capable' bit for all hotpluggable CPUs except the - * first/boot CPU. Cold-booted CPUs without 'Id' can also be unplugged. - * Though as-of-now this is only used as a debugging feature. + * The ARM GIC CPU Interface can be either 'online-capable' or 'enabled' at + * boot. We MUST set the 'online-capable' bit for all hotpluggable CPUs. * - * UEFI ACPI Specification 6.5 - * Section: 5.2.12.14. GIC CPU Interface (GICC) Structure - * Table: 5.37 GICC CPU Interface Flags - * Link: https://uefi.org/specs/ACPI/6.5 + * Change Link: https://bugzilla.tianocore.org/show_bug.cgi?id=3706 + * + * Refer to the UEFI ACPI Specification 6.5: + * Section: 5.2.12.14. GIC CPU Interface (GICC) Structure + * Table: 5.37 GICC CPU Interface Flags + * Link: https://uefi.org/specs/ACPI/6.5 + * + * Cold-booted CPUs, except for the first/boot CPU, SHOULD be allowed to be + * hot(un)plugged as well. However, for this to happen, these CPUs MUST have + * the 'online-capable' bit set. This creates a compatibility problem with + * legacy OS, as it might ignore 'online-capable' bits during boot time, and + * hence some CPUs might not get detected. + * + * To fix this, the MADT GIC CPU interface flag should allow both + * 'online-capable' and 'enabled' bits to be set together. This change will + * require an update to the UEFI ACPI standard. Until this update occurs, + * all cold-booted CPUs should be exposed as 'enabled' only. */ - return cpu && !cpu->cpu_index ? 1 : (1 << 3); + return cpu && cpu->cold_booted ? 1 : (1 << 3); } static void diff --git a/hw/arm/virt.c b/hw/arm/virt.c index a2200099a1..770b599acf 100644 --- a/hw/arm/virt.c +++ b/hw/arm/virt.c @@ -3163,6 +3163,10 @@ static void virt_cpu_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev, * This shall be used during the init of ACPI Hotplug state and hot-unplug */ cs->acpi_persistent = true; + + if (!dev->hotplugged) { + cs->cold_booted = true; + } } static void virt_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev, @@ -3223,6 +3227,18 @@ static void virt_cpu_unplug_request(HotplugHandler *hotplug_dev, return; } + /* + * UEFI ACPI standard change is required to make both 'enabled' and the + * 'online-capable' bit co-exist instead of being mutually exclusive. + * check virt_acpi_get_gicc_flags() for more details. + * + * Disable the unplugging of cold-booted vCPUs as a temporary mitigation. + */ + if (cs->cold_booted) { + error_setg(errp, "Hot-unplug of cold-booted CPU not supported!"); + return; + } + if (cs->cpu_index == first_cpu->cpu_index) { error_setg(errp, "Boot CPU(id%d=%d:%d:%d:%d) hot-unplug not supported", first_cpu->cpu_index, cpu->socket_id, cpu->cluster_id, diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index e13e542177..99b699b47f 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -556,6 +556,8 @@ struct CPUState { uint32_t halted; int32_t exception_index; + bool cold_booted; + AccelCPUState *accel; /* Used to keep track of an outstanding cpu throttle thread for migration -- 2.34.1
