On Tue, Sep 07, 2021 at 12:52:54PM +0100, Dr. David Alan Gilbert wrote: > * Daniel P. Berrangé (berrange@xxxxxxxxxx) 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? > > > > IIUC you can only reach scenario (3) if you have created a guest > > using '-object sev-snp-guest', which is a new feature introduced > > in patch 2. > > > > IOW, scenario (3) old mgmt app + new QEMU + sev-snp guest does > > not exist as a combination. Thus the (bad) field is actually (n/a) > > > > So I believe this proposed change is acceptable in all scenarios > > with existing deployed usage, as well as all newly introduced > > scenarios. > > I wonder if it's worth going firther and renaming 'policy' in the > SNP world to 'snppolicy' just to reduce the risk of accidentally > specifying the wrong one. Seems reasonable. I'll plan on renaming to 'snp-policy' if there are no objections. > > Dave > > > Regards, > > Daniel > > -- > > |: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fberrange.com%2F&data=04%7C01%7Cmichael.roth%40amd.com%7Cb9a484cd5d4f484b542908d971f61073%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637666123947391605%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=D56oHIuVk%2FmAJaKYtpJ3ZEZpKZpDPWZXydV3tpYjcM4%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%7Cb9a484cd5d4f484b542908d971f61073%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637666123947401567%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=A9YA65nj6En3f3E2wm%2BVZE%2F6DpdbDKyHSWN9VXHAk8U%3D&reserved=0 :| > > |: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flibvirt.org%2F&data=04%7C01%7Cmichael.roth%40amd.com%7Cb9a484cd5d4f484b542908d971f61073%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637666123947401567%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=yf%2FV3f3%2FNxEDwmYESp7D0ZOn74aM6cXskVJrvHLvXRE%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%7Cb9a484cd5d4f484b542908d971f61073%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637666123947401567%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=pUYNVu6WWgPtwjwrjvz3YCCY7S1Qli%2FfvQKmkaRu3gc%3D&reserved=0 :| > > |: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fentangle-photo.org%2F&data=04%7C01%7Cmichael.roth%40amd.com%7Cb9a484cd5d4f484b542908d971f61073%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637666123947401567%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=opdXI%2BlyzxWhUbNNgka6sMKMiLmMHfk8WuZY6cMy7yE%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%7Cb9a484cd5d4f484b542908d971f61073%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637666123947401567%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=8cV6tsleO5nDBVKR3WX74a%2BKch5RdRdmPciv%2F6T9nOg%3D&reserved=0 :| > > > -- > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK >
