(+Daniel, +Rich) On 02/23/22 17:08, Jason A. Donenfeld wrote: > On Wed, Feb 23, 2022 at 2:12 PM Jason A. Donenfeld <ja...@zx2c4.com> wrote: >> second patch is the reason this is just an RFC: it's a cleanup of the >> ACPI driver from last year, and I don't really have much experience >> writing, testing, debugging, or maintaining these types of drivers. >> Ideally this thread would yield somebody saying, "I see the intent of >> this; I'm happy to take over ownership of this part." That way, I can >> focus on the RNG part, and whoever steps up for the paravirt ACPI part >> can focus on that. > > I actually managed to test this in QEMU, and it seems to work quite well. > Steps: > > $ qemu-system-x86_64 ... -device vmgenid,guid=auto -monitor stdio > (qemu) savevm blah > (qemu) quit > $ qemu-system-x86_64 ... -device vmgenid,guid=auto -monitor stdio > (qemu) loadvm blah > > Doing this successfully triggers the function to reinitialize the RNG > with the new GUID.
QEMU's related design is documented in <https://git.qemu.org/?p=qemu.git;a=blob;f=docs/specs/vmgenid.txt>. The Microsoft specification referenced therein, <http://go.microsoft.com/fwlink/?LinkId=260709>, contains the following statement: "they can also use the data provided in the 128-bit identifier as a high entropy random data source" So reinitializing an RNG from it is an express purpose. More info in the libvirt docs (see "genid"): https://libvirt.org/formatdomain.html#general-metadata QEMU's interpretation of the VMGENID specifically as a UUID (which I believe comes from me) has received (valid) criticism since: https://github.com/libguestfs/virt-v2v/blob/master/docs/vm-generation-id-across-hypervisors.txt (This document also investigates VMGENID on other hypervisors, which I think pertains to your other message.) > (It appears there's a bug in QEMU which prevents > the GUID from being reinitialized when running `loadvm` without > quitting first; I suppose this should be discussed with QEMU > upstream.) That's not (necessarily) a bug; see the end of the above-linked QEMU document: "There are no known use cases for changing the GUID once QEMU is running, and adding this capability would greatly increase the complexity." > > So that's very positive. But I would appreciate hearing from some > ACPI/Virt/Amazon people about this. I've only made some random comments; I didn't see a question so I couldn't attempt to answer :) Thanks Laszlo
