On Mon, 2024-04-08 at 18:51 +0000, Sean Christopherson wrote: > Off topic, any chance I can bribe/convince you to wrap your email replies > closer > to 80 chars, not 100? Yeah, checkpath no longer complains when code exceeds > 80 > chars, but my brain is so well trained for 80 that it actually slows me down a > bit when reading mails that are wrapped at 100 chars. Heh, sure. I was trying 100 chars recently as an experiment to better quote code in mails. I was also getting thrown a little. > > > Or are you suggesting that KVM should look at the value of > > CPUID(0X8000_0008).eax[23:16] passed from > > userspace? > > This. Note, my pseudo-patch incorrectly looked at bits 15:8, that was just me > trying to go off memory. > > > I'm not following the code examples involving struct kvm_vcpu. Since TDX > > configures these at a VM level, there isn't a vcpu. > > Ah, I take it GPAW is a VM-scope knob? Yea. > I forget where we ended up with the ordering > of TDX commands vs. creating vCPUs. Does KVM allow creating vCPU structures > in > advance of the TDX INIT call? If so, the least awful solution might be to use > vCPU0's CPUID. Currently the values for the directly settable CPUID leafs come via a TDX specific init VM userspace API. There was some discussion on forcing the values provided there to be consistent with the CPUIDs set on the VCPUs later: https://lore.kernel.org/lkml/ZDbMuZKhAUbrkrc7@xxxxxxxxxx/ Which lead to: https://lore.kernel.org/kvm/ac424b167210288cdf32ac940bcc6ec84f8a45b9.1708933498.git.isaku.yamahata@xxxxxxxxx/ https://lore.kernel.org/kvm/d394938197044b40bbe6d9ce2402f72a66a99e80.1708933498.git.isaku.yamahata@xxxxxxxxx/ So KVM has to reject KVM_SET_CPUID if it doesn't match the VM-wide configuration anyway, however the VM-scoped CPUID state ends up getting configured. Then if we leave the VM-scoped CPUID configuration with the VM-scoped operations it doesn't force KVM_SET_CPUID to learn about rejecting TDX incompatible CPUID state (state that is not directly configurable). So should we look at making the TDX side follow a KVM_GET_SUPPORTED_CPUID/KVM_SET_CPUID pattern for feature enablement? Or am I misreading general guidance out of this specific suggestion around GPAW?
