On Fri, Sep 03, 2021 at 04:30:48PM +0100, Daniel P. Berrangé wrote: > On Fri, Sep 03, 2021 at 10:13:16AM -0500, Michael Roth wrote: > > On Wed, Sep 01, 2021 at 04:14:10PM +0200, Markus Armbruster wrote: > > > Michael Roth <michael.roth@xxxxxxx> writes: > > > > > > > Most of the current 'query-sev' command is relevant to both legacy > > > > SEV/SEV-ES guests and SEV-SNP guests, with 2 exceptions: > > > > > > > > - 'policy' is a 64-bit field for SEV-SNP, not 32-bit, and > > > > the meaning of the bit positions has changed > > > > - 'handle' is not relevant to SEV-SNP > > > > > > > > To address this, this patch adds a new 'sev-type' field that can be > > > > used as a discriminator to select between SEV and SEV-SNP-specific > > > > fields/formats without breaking compatibility for existing management > > > > tools (so long as management tools that add support for launching > > > > SEV-SNP guest update their handling of query-sev appropriately). > > > > > > Technically a compatibility break: query-sev can now return an object > > > that whose member @policy has different meaning, and also lacks @handle. > > > > > > Matrix: > > > > > > Old mgmt app New mgmt app > > > Old QEMU, SEV/SEV-ES good good(1) > > > New QEMU, SEV/SEV-ES good(2) good > > > New QEMU, SEV-SNP bad(3) good > > > > > > Notes: > > > > > > (1) As long as the management application can cope with absent member > > > @sev-type. > > > > > > (2) As long as the management application ignores unknown member > > > @sev-type. > > > > > > (3) Management application may choke on missing member @handle, or > > > worse, misinterpret member @policy. Can only happen when something > > > other than the management application created the SEV-SNP guest (or the > > > user somehow made the management application create one even though it > > > doesn't know how, say with CLI option passthrough, but that's always > > > fragile, and I wouldn't worry about it here). > > > > > > I think (1) and (2) are reasonable. (3) is an issue for management > > > applications that support attaching to existing guests. Thoughts? > > > > Hmm... yah I hadn't considering 'old mgmt' trying to interact with a SNP > > guest started through some other means. > > > > Don't really see an alternative other than introducing a new > > 'query-sev-snp', but that would still leave 'old mgmt' broken, since > > it might still call do weird stuff like try to interpret the SNP policy > > as an SEV/SEV-ES and end up with some very unexpected results. So if I > > did go this route, I would need to have QMP begin returning an error if > > query-sev is run against an SNP guest. But currently for non-SEV guests > > it already does: > > > > error_setg(errp, "SEV feature is not available") > > > > so 'old mgmt' should be able to handle the error just fine. > > > > Would that approach be reasonable? > > This ties into the question I've just sent in my other mail. > > If the hardware strictly requires that guest are created in SEV-SNP > mode only, and will not support SEV/SEV-ES mode, then we need to > ensure "query-sev" reports the feature as not-available, so that > existing mgmt apps don't try to use SEV/SEV-ES. An SEV-SNP-capable host can run both 'legacy' SEV/SEV-ES, as well as SEV-SNP guests, at the same time. But as far as QEMU goes, we need to specify one or the other explicitly at launch time, via existing 'sev-guest', or the new 'sev-snp-guest' ConfidentialGuestSupport type. > > If the SEV-SNP hardware is functionally back-compatible with a gues > configured in SEV/SEV-ES mode, then we souldn't need a new command, > just augment th eexisting command with additional field(s), to > indicate existance of SEV-SNP features. query-sev-info provides information specific to the guest instance, like the configured policy. Are you thinking of query-sev-capabilities, which reports some host-wide information and should indeed remain available for either case. (and maybe should also be updated to report on SEV-SNP availability for the host?) > > Regards, > Daniel > -- > |: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fberrange.com%2F&data=04%7C01%7Cmichael.roth%40amd.com%7C86e4ceb7f55f4cf839e708d96eefd768%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637662798671249591%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=Fo%2FCcCEG7OrpVNj2ij2CzYJCMFXs30YUnRaClz17Okc%3D&reserved=0 -o- https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.flickr.com%2Fphotos%2Fdberrange&data=04%7C01%7Cmichael.roth%40amd.com%7C86e4ceb7f55f4cf839e708d96eefd768%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637662798671249591%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ypMyoiFFTmgWnDD3UwJrKIcHGzDaKQ8nXnFASw7gyRE%3D&reserved=0 :| > |: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flibvirt.org%2F&data=04%7C01%7Cmichael.roth%40amd.com%7C86e4ceb7f55f4cf839e708d96eefd768%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637662798671249591%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=viWBuUPauLi41pEKT143wh0Ds%2FwJqIG%2BDfraIO5uxNE%3D&reserved=0 -o- https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ffstop138.berrange.com%2F&data=04%7C01%7Cmichael.roth%40amd.com%7C86e4ceb7f55f4cf839e708d96eefd768%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637662798671249591%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=H%2BTFPox5kDO4osMWicvwUrb8PvNfMBPLwCWEiEfcIOw%3D&reserved=0 :| > |: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fentangle-photo.org%2F&data=04%7C01%7Cmichael.roth%40amd.com%7C86e4ceb7f55f4cf839e708d96eefd768%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637662798671259556%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=9mp0c7dJ07EIdYYNZ73DQ6ax%2Bw0ORKTpScI6p5gNpVo%3D&reserved=0 -o- https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.instagram.com%2Fdberrange&data=04%7C01%7Cmichael.roth%40amd.com%7C86e4ceb7f55f4cf839e708d96eefd768%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637662798671259556%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=%2FL1f9LxzAqXxVNbUhWa4w2Sibb6f0vLcRzaM2%2F9NY90%3D&reserved=0 :| >
