From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34334) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bn3TN-0001JO-8h for qemu-devel@nongnu.org; Thu, 22 Sep 2016 08:51:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bn3TJ-0005Aj-D0 for qemu-devel@nongnu.org; Thu, 22 Sep 2016 08:51:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60564) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bn3TJ-0005AZ-6v for qemu-devel@nongnu.org; Thu, 22 Sep 2016 08:51:25 -0400 From: Igor Mammedov Date: Thu, 22 Sep 2016 14:50:52 +0200 Message-Id: <1474548655-157373-12-git-send-email-imammedo@redhat.com> In-Reply-To: <1474548655-157373-1-git-send-email-imammedo@redhat.com> References: <1474548655-157373-1-git-send-email-imammedo@redhat.com> Subject: [Qemu-devel] [PATCH v2 11/14] pc: clarify FW_CFG_MAX_CPUS usage comment List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: rkrcmar@redhat.com, ehabkost@redhat.com, mst@redhat.com, kevin@koconnor.net, pbonzini@redhat.com, lersek@redhat.com, chao.gao@intel.com, peterx@redhat.com, liuxiaojian6@huawei.com Signed-off-by: Igor Mammedov --- hw/i386/pc.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index f1c1013..f807932 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -746,17 +746,15 @@ static FWCfgState *bochs_bios_init(AddressSpace *as, PCMachineState *pcms) /* FW_CFG_MAX_CPUS is a bit confusing/problematic on x86: * - * SeaBIOS needs FW_CFG_MAX_CPUS for CPU hotplug, but the CPU hotplug - * QEMU<->SeaBIOS interface is not based on the "CPU index", but on the APIC - * ID of hotplugged CPUs[1]. This means that FW_CFG_MAX_CPUS is not the - * "maximum number of CPUs", but the "limit to the APIC ID values SeaBIOS - * may see". + * For machine types prior to 1.8, SeaBIOS needs FW_CFG_MAX_CPUS for + * building MPTable, ACPI MADT, ACPI CPU hotplug and ACPI SRAT table, + * that tables are based on xAPIC ID and QEMU<->SeaBIOS interface + * for CPU hotplug also uses APIC ID and not "CPU index". + * This means that FW_CFG_MAX_CPUS is not the "maximum number of CPUs", + * but the "limit to the APIC ID values SeaBIOS may see". * - * So, this means we must not use max_cpus, here, but the maximum possible - * APIC ID value, plus one. - * - * [1] The only kind of "CPU identifier" used between SeaBIOS and QEMU is - * the APIC ID, not the "CPU index" + * So for compatibility reasons with old BIOSes we are stuck with + * "etc/max-cpus" actually being apic_id_limit */ fw_cfg_add_i16(fw_cfg, FW_CFG_MAX_CPUS, (uint16_t)pcms->apic_id_limit); fw_cfg_add_i64(fw_cfg, FW_CFG_RAM_SIZE, (uint64_t)ram_size); -- 2.7.4