From 9953f8822cc316eec9962f0a2858c3439a80adec Mon Sep 17 00:00:00 2001 From: Markus Armbruster Date: Fri, 12 Apr 2013 17:25:03 +0200 Subject: pc: Kill the "use flash device for BIOS unless KVM" misfeature 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 Message-id: 1365780303-26398-4-git-send-email-armbru@redhat.com Signed-off-by: Anthony Liguori --- hw/i386/pc_piix.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'hw/i386/pc_piix.c') diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c index 13e1d50..89b4cb4 100644 --- a/hw/i386/pc_piix.c +++ b/hw/i386/pc_piix.c @@ -235,9 +235,16 @@ static void pc_init_pci(QEMUMachineInitArgs *args) 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); } @@ -246,6 +253,7 @@ static void pc_init_pci_1_2(QEMUMachineInitArgs *args) { disable_kvm_pv_eoi(); enable_compat_apic_id_mode(); + pc_sysfw_flash_vs_rom_bug_compatible = true; pc_init_pci(args); } @@ -318,7 +326,7 @@ static QEMUMachine pc_i440fx_machine_v1_5 = { 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, -- cgit v1.1