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authorMarkus Armbruster <armbru@redhat.com>2013-04-12 17:25:03 +0200
committerAnthony Liguori <aliguori@us.ibm.com>2013-04-24 13:23:51 -0500
commit9953f8822cc316eec9962f0a2858c3439a80adec (patch)
treebf8e999fa32255d6bac73f24f4c41ef35838fecd /hw/block
parent6fd028f64f662c801fd5a54d0e3a1d2baeee93ea (diff)
downloadhqemu-9953f8822cc316eec9962f0a2858c3439a80adec.zip
hqemu-9953f8822cc316eec9962f0a2858c3439a80adec.tar.gz
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 <armbru@redhat.com> Message-id: 1365780303-26398-4-git-send-email-armbru@redhat.com Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'hw/block')
-rw-r--r--hw/block/pc_sysfw.c20
1 files changed, 18 insertions, 2 deletions
diff --git a/hw/block/pc_sysfw.c b/hw/block/pc_sysfw.c
index 0d95c8a..aad8614 100644
--- a/hw/block/pc_sysfw.c
+++ b/hw/block/pc_sysfw.c
@@ -194,11 +194,23 @@ static void old_pc_system_rom_init(MemoryRegion *rom_memory)
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));
@@ -212,7 +224,11 @@ void pc_system_firmware_init(MemoryRegion *rom_memory)
/* 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);
@@ -239,7 +255,7 @@ void pc_system_firmware_init(MemoryRegion *rom_memory)
}
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(),
};
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