> > > On Tue, May 18, 2021, Reiji Watanabe wrote: > > > > BTW, I would think having a default CPUID for CPUID.(EAX=0x1) would be better > > > > for consistency of a vCPU state for RESET. I would think it doesn't matter > > > > practically anyway though. > > > > > > Probably, but that would require defining default values for all of CPUID.0x0 and > > > CPUID.0x1, which is a can of worms I'd rather not open. E.g. vendor info, basic > > > feature set, APIC ID, etc... would all need default values. On the other hand, > > > the EDX value stuffing predates CPUID, so using 0x600 isn't provably wrong, just > > > a bit anachronistic. :-) > > > > I see... Then I don't think it's worth doing... > > Just out of curiosity, can't we simply use a vcpu_id for the APIC ID ? > > That would mostly work, but theoretically we could overflow the 8 bit field > because max vCPUs is 288. Thanks Larrabee. > > commit 682f732ecf7396e9d6fe24d44738966699fae6c0 > Author: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Date: Tue Jul 12 22:09:29 2016 +0200 > > KVM: x86: bump MAX_VCPUS to 288 > > 288 is in high demand because of Knights Landing CPU. > We cannot set the limit to 640k, because that would be wasting space. > > > Also, can't we simply use the same values that KVM_GET_SUPPORTED_CPUID > > provides for other CPUID fields ? > > Yes, that would mostly work. It's certainly possible to have a moderately sane > default, but there's essentially zero benefit in doing so since practically > speaking all userspace VMMs will override CPUID anyways. KVM could completely > default to the host CPUID, but again, it wouldn't provide any meaningful benefit, > while doing so would step on userspace's toes since KVM's approach is that KVM is > "just" an accelerator, while userspace defines the CPU model, devices, etc... > And it would also mean KVM has to start worrying about silly corner cases like > the max vCPUs thing. That's why I say it's a can of worms :-) Ah, I see. Thank you for the answer and the helpful information ! Regards, Reiji
