From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33928) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bwpdN-00089c-8j for qemu-devel@nongnu.org; Wed, 19 Oct 2016 08:06:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bwpdJ-0003KJ-9H for qemu-devel@nongnu.org; Wed, 19 Oct 2016 08:06:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55604) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1bwpdJ-0003K8-3p for qemu-devel@nongnu.org; Wed, 19 Oct 2016 08:06:09 -0400 From: Igor Mammedov Date: Wed, 19 Oct 2016 14:05:39 +0200 Message-Id: <1476878743-144953-10-git-send-email-imammedo@redhat.com> In-Reply-To: <1476878743-144953-1-git-send-email-imammedo@redhat.com> References: <1476878743-144953-1-git-send-email-imammedo@redhat.com> Subject: [Qemu-devel] [PATCH v4 09/13] 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: kraxel@redhat.com, ehabkost@redhat.com, liuxiaojian6@huawei.com, mst@redhat.com, rkrcmar@redhat.com, peterx@redhat.com, kevin@koconnor.net, pbonzini@redhat.com, lersek@redhat.com, chao.gao@intel.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 6f4075f..4b97795 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