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[Qemu-devel] [PATCH v4 09/13] pc: clarify FW_CFG_MAX_CPUS usage comment
From: |
Igor Mammedov |
Subject: |
[Qemu-devel] [PATCH v4 09/13] pc: clarify FW_CFG_MAX_CPUS usage comment |
Date: |
Wed, 19 Oct 2016 14:05:39 +0200 |
Signed-off-by: Igor Mammedov <address@hidden>
---
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
- [Qemu-devel] [PATCH v4 01/13] pc: acpi: x2APIC support for MADT table and _MAT method, (continued)
- [Qemu-devel] [PATCH v4 01/13] pc: acpi: x2APIC support for MADT table and _MAT method, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 06/13] pc: apic_common: restore APIC ID to initial ID on reset, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 05/13] pc: apic_common: extend APIC ID property to 32bit, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 04/13] pc: leave max apic_id_limit only in legacy cpu hotplug code, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 08/13] pc: kvm_apic: pass APIC ID depending on xAPIC/x2APIC mode, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 07/13] pc: apic_common: reset APIC ID to initial ID when switching into x2APIC mode, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 09/13] pc: clarify FW_CFG_MAX_CPUS usage comment,
Igor Mammedov <=
- [Qemu-devel] [PATCH v4 10/13] increase MAX_CPUMASK_BITS from 255 to 288, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 12/13] pc: require IRQ remapping and EIM if there could be x2APIC CPUs, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 13/13] pc: q35: bump max_cpus to 288, Igor Mammedov, 2016/10/19
- [Qemu-devel] [PATCH v4 11/13] pc: add 'etc/boot-cpus' fw_cfg file for machine with more than 255 CPUs, Igor Mammedov, 2016/10/19