Hotpluggable CPUs MUST be exposed as 'online-capable' as per the new change. But cold booted CPUs if made 'online-capable' during boot time might not get detected in the legacy OS. Hence, can cause compatibility problems.
Original Change Link: https://bugzilla.tianocore.org/show_bug.cgi?id=3706 Specification change might take time and hence disabling the support of unplugging any cold booted CPUs to preserve the compatibility with legacy OS. Signed-off-by: Salil Mehta <salil.me...@huawei.com> --- hw/arm/virt-acpi-build.c | 19 ++++++++++++++----- hw/arm/virt.c | 16 ++++++++++++++++ include/hw/core/cpu.h | 2 ++ 3 files changed, 32 insertions(+), 5 deletions(-) diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c index 377450dd16..879c83a337 100644 --- a/hw/arm/virt-acpi-build.c +++ b/hw/arm/virt-acpi-build.c @@ -710,17 +710,26 @@ 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. + * ARM GIC CPU Interface can be 'online-capable' or 'enabled' at boot. We + * MUST set 'online-capable' bit for all hotpluggable CPUs. + * Change Link: https://bugzilla.tianocore.org/show_bug.cgi?id=3706 * * 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)plug as well but for this to happen these MUST have + * 'online-capable' bit set. Later creates 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 MADT GIC CPU interface flag + * should be allowed to have both bits set i.e. 'online-capable' and + * 'Enabled' bits together. This change will require UEFI ACPI standard + * change. Till this happens exposing all cold-booted CPUs 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 e46f529801..3bfe9b9db3 100644 --- a/hw/arm/virt.c +++ b/hw/arm/virt.c @@ -3151,6 +3151,10 @@ 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, @@ -3214,6 +3218,18 @@ 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 ffd815a0d8..f6b92a3285 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -441,6 +441,8 @@ struct CPUState { uint32_t can_do_io; int32_t exception_index; + bool cold_booted; + AccelCPUState *accel; /* shared by kvm, hax and hvf */ bool vcpu_dirty; -- 2.34.1