On Tue, Jun 25, 2019 at 05:26:03PM +0100, Daniel P. Berrangé wrote: > On Tue, Jun 25, 2019 at 02:00:06AM -0300, Eduardo Habkost wrote: > > Base code for versioned CPU models. This will register a "-4.1" > > version of all existing CPU models, and make the unversioned CPU > > models be an alias for the -4.1 versions on the pc-*-4.1 machine > > types. > > > > On older machine types, the unversioned CPU models will keep the > > old behavior. This way, management software can use old machine > > types while resolving aliases if compatibility with older QEMU > > versions is required. > > > > Using "-machine none", the unversioned CPU models will be aliases > > to the latest CPU model version. > > > > Includes a test case to ensure that: > > old machine types won't report any alias to versioned CPU models; > > "pc-*-4.1" will return aliases to -4.1 CPU models; > > and "-machine none" will report aliases to some versioned CPU model. > > I'm wondering about the of tieing CPU versions to the release version > number and whether its a good idea or not ? > > Could there be a reason for us to introduce 2 or more variants > of a CPU in the same release & would that be a problem if we needed > todo it ?
I don't see a problem, we can use 3-digit versions that won't be enabled by any machine type by default. > > Consider if we did not have a Broadwell CPU model defined yet > and we were adding it at the same time as Spectre came out. We > might have needed to add "Broadwell-NN" and "Broadwell-MM" one > with "spec-ctrl" and one without, in order to ensure runability > on hosts with & without the microcode upgrade. "Broadwell" alias > would resolve to either the NN or MM variant according to what > the current host supported. > > One way to cope with that would have been to add a 3rd digit > after the version number. eg a Broadwell-4.1.1 and Broadwell-4.1.2 That's exactly what I did for Cascadelake-Server, see patch 6/6. > > An alternative could consider using a plain counter for the CPU > versions eg Broadwell-1, Broadwell-2, etc.... ? This is possible too. It would require a more complex mapping between machine types and CPU model versions, though. Maybe this is worth the extra complexity because it would make the external interfaces simpler. > > > If we want to backport the newly added CPU model variants to > exist branches, plain counters don't have the unsightly mismatch. > eg we'd backport Broadwell-3 to QEMU 3.1, not Broadwell-4.1 to > QEMU 3.1. This isn't a functional problem, just something looking > a bit odd. I think I'm liking this approach. If we're untying CPU models from machine types, let's do it all the way. -- Eduardo
