Use of a flash memory device for the BIOS was added in series "[PATCH
v10 0/8] PC system flash support", commit
4732dca..
1b89faf, v1.1.
Flash vs. ROM is a guest-visible difference. Thus, flash use had to
be suppressed for machine types pc-1.0 and older. This was
accomplished by adding a dummy device "pc-sysfw" with property
"rom_only":
* Non-zero rom_only means "use ROM". Default for pc-1.0 and older.
* Zero rom_only means "maybe use flash". Default for newer machines.
Not only is the dummy device ugly, it was also retroactively added to
the older machine types! Fortunately, it's not guest-visible (thus no
immediate guest ABI breakage), and has no vmstate (thus no immediate
migration breakage). Breakage occurs only if the user unwisely
enables flash by setting rom_only to zero. Patch review FAIL #1.
Why "maybe use flash"? Flash didn't (and still doesn't) work with
KVM. Therefore, rom_only=0 really means "use flash, except when KVM
is enabled, use ROM". This is a Bad Idea, because it makes enabling/
disabling KVM guest-visible. Patch review FAIL #2.
Aside: it also precludes migrating between KVM on and off, but that's
not possible for other reasons anyway.
Fix as follows:
1. Change the meaning of rom_only=0 to mean "use flash, no ifs, buts,
or maybes" for pc-i440fx-1.5 and pc-q35-1.5. Don't change anything
for older machines (to remain bug-compatible).
2. Change the default value from 0 to 1 for these machines.
Necessary, because 0 doesn't work with KVM. Once it does, we can flip
the default back to 0.
3. Don't revert the retroactive addition of device "pc-sysfw" to older
machine types. Seems not worth the trouble.
4. Add a TODO comment asking for device "pc-sysfw" to be dropped once
flash works with KVM.
Net effect is that you get a BIOS ROM again even when KVM is disabled,
just like for machines predating the introduction of flash.
To get flash instead, use "--global pc-sysfw.rom_only=0".
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-id:
1365780303-26398-4-git-send-email-armbru@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
bios);
}
+/*
+ * Bug-compatible flash vs. ROM selection enabled?
+ * A few older machines enable this.
+ */
+bool pc_sysfw_flash_vs_rom_bug_compatible;
+
void pc_system_firmware_init(MemoryRegion *rom_memory)
{
DriveInfo *pflash_drv;
PcSysFwDevice *sysfw_dev;
+ /*
+ * TODO This device exists only so that users can switch between
+ * use of flash and ROM for the BIOS. The ability to switch was
+ * created because flash doesn't work with KVM. Once it does, we
+ * should drop this device for new machine types.
+ */
sysfw_dev = (PcSysFwDevice*) qdev_create(NULL, "pc-sysfw");
qdev_init_nofail(DEVICE(sysfw_dev));
/* Currently KVM cannot execute from device memory.
Use old rom based firmware initialization for KVM. */
- if (kvm_enabled()) {
+ /*
+ * This is a Bad Idea, because it makes enabling/disabling KVM
+ * guest-visible. Do it only in bug-compatibility mode.
+ */
+ if (pc_sysfw_flash_vs_rom_bug_compatible && kvm_enabled()) {
if (pflash_drv != NULL) {
fprintf(stderr, "qemu: pflash cannot be used with kvm enabled\n");
exit(1);
}
static Property pcsysfw_properties[] = {
- DEFINE_PROP_UINT8("rom_only", PcSysFwDevice, rom_only, 0),
+ DEFINE_PROP_UINT8("rom_only", PcSysFwDevice, rom_only, 1),
DEFINE_PROP_END_OF_LIST(),
};
initrd_filename, cpu_model, 1, 1);
}
+static void pc_init_pci_1_4(QEMUMachineInitArgs *args)
+{
+ pc_sysfw_flash_vs_rom_bug_compatible = true;
+ pc_init_pci(args);
+}
+
static void pc_init_pci_1_3(QEMUMachineInitArgs *args)
{
enable_compat_apic_id_mode();
+ pc_sysfw_flash_vs_rom_bug_compatible = true;
pc_init_pci(args);
}
{
disable_kvm_pv_eoi();
enable_compat_apic_id_mode();
+ pc_sysfw_flash_vs_rom_bug_compatible = true;
pc_init_pci(args);
}
static QEMUMachine pc_i440fx_machine_v1_4 = {
.name = "pc-i440fx-1.4",
.desc = "Standard PC (i440FX + PIIX, 1996)",
- .init = pc_init_pci,
+ .init = pc_init_pci_1_4,
.max_cpus = 255,
.compat_props = (GlobalProperty[]) {
PC_COMPAT_1_4,
}
}
+static void pc_q35_init_1_4(QEMUMachineInitArgs *args)
+{
+ pc_sysfw_flash_vs_rom_bug_compatible = true;
+ pc_q35_init(args);
+}
+
static QEMUMachine pc_q35_machine_v1_5 = {
.name = "pc-q35-1.5",
.alias = "q35",
static QEMUMachine pc_q35_machine_v1_4 = {
.name = "pc-q35-1.4",
.desc = "Standard PC (Q35 + ICH9, 2009)",
- .init = pc_q35_init,
+ .init = pc_q35_init_1_4,
.max_cpus = 255,
.compat_props = (GlobalProperty[]) {
PC_COMPAT_1_4,
}
/* pc_sysfw.c */
+extern bool pc_sysfw_flash_vs_rom_bug_compatible;
void pc_system_firmware_init(MemoryRegion *rom_memory);
/* e820 types */
.driver = "virtio-net-pci",\
.property = "romfile",\
.value = "pxe-virtio.rom",\
+ },{\
+ .driver = "pc-sysfw",\
+ .property = "rom_only",\
+ .value = stringify(0),\
}
#endif