Sean, Your response did not land in my mailbox for some reason. Replying using In-reply-to option. >Hrm, is MSR_AMD64_VIRT_SPEC_CTRL only for SSBD? Should that MSR be renamed to >avoid confusion with the new form of VIRT_SPEC_CTRL? We can rename it to MSR_AMD64_VIRT_SSBD_SPEC_CTRL if that is any better. >Well, it's still required if the hypervisor wanted to allow the guest to turn >off mitigations that are enabled in the host. I'd omit this entirely and focus >on what hardware does and how Linux/KVM utilize the new feature. Ok. Sure. >This line needs to be higher in the changelog, it's easily the most relevant >info for understanding the mechanics. Please also explicitly state the context >switching mechanics, e.g. is it tracked in the VMCB, loaded on VMRUN, saved on >VM-Exit, etc... Will add more details. >This will break migration, or maybe just cause wierdness, as userspace will >always see '0' when reading SPEC_CTRL and its writes will be ignored. Is there >a VMCB field that holds the guest's value? If so, this read can be skipped, and >instead the MSR set/get flows probably need to poke into the VMCB. Yes. The guest SEPC_CTRL value is saved in VMCB save area(i.e. 0x400 + 0x2E0). Yes, will look into setting VMCB with the desired values in msr set/get if that helps. Thanks Babu
