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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> |
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| .. | ||
| kvm | ||
| kvmvapic.c | ||
| Makefile.objs | ||
| multiboot.c | ||
| multiboot.h | ||
| pc_piix.c | ||
| pc_q35.c | ||
| pc.c | ||
| smbios.c | ||
| xen_domainbuild.c | ||
| xen_domainbuild.h | ||
| xen_machine_pv.c | ||