2011/3/8 Gleb Natapov <g...@redhat.com>: > On Tue, Mar 08, 2011 at 07:18:09AM +0000, Stefan Hajnoczi wrote: >> > Regarding the non-volatile variables issue, I have been trying to >> > develop a proposal for addressing this with a change to QEMU's >> > hardware support of bios.bin. But, I don't have the suggestion (or >> > implementation) ready at this time. >> >> Sounds like something to keep discussing with the QEMU and SeaBIOS >> communities. Gleb Natapov and Kevin O'Connor have done a lot of the >> recent BIOS and firmware interface work. I think persistent CMOS has >> come up several times and might be similar to non-volatile UEFI >> storage. >> > What kind of information OVMF stores on a persistent storage?
Non-volatile variables are a general system wide environment variable storage facility, but one key thing to store (for instance) is the path to the boot image. > CMOS > memory is less them 512 byte IIRC and this may not be enough. What OVMF > uses on real HW for non-volatile storage? Regarding CMOS, I think qemu exposes 128 bytes of non persistent CMOS RAM. Many current chipsets provide another bank of 128 bytes, meaning a total of 256 bytes (minus the RTC registers). Regarding UEFI non-volatile variables on real HW: Most systems today have at least 1MB of flash storage located just below 4GB. The entire contents can be modified, which is how firmware updates happen. For a UEFI based system, the non-volatile variables generally occupy 8KB~64KB of the flash depending on flash space availability. -Jordan