On Tue, Aug 02, 2022 at 06:55:48PM +0800, Xiaoyao Li wrote: > On 8/2/2022 5:49 PM, Daniel P. Berrangé wrote: > > On Tue, Aug 02, 2022 at 03:47:10PM +0800, Xiaoyao Li wrote: > > > > - CPU model > > > > > > We cannot create a TD with arbitrary CPU model like what for non-TDX VMs, > > > because only a subset of features can be configured for TD. > > > - It's recommended to use '-cpu host' to create TD; > > > - '+feature/-feature' might not work as expected; > > > > > > future work: To introduce specific CPU model for TDs and enhance +/-features > > > for TDs. > > > > Which features are incompatible with TDX ? > > TDX enforces some features fixed to 1 (e.g., CPUID_EXT_X2APIC, > CPUID_EXT_HYPERVISOR)and some fixed to 0 (e.g., CPUID_EXT_VMX ). > > Details can be found in patch 8 and TDX spec chapter "CPUID virtualization" > > > Presumably you have such a list, so that KVM can block them when > > using '-cpu host' ? > > No, KVM doesn't do this. The result is no error reported from KVM but what > TD OS sees from CPUID might be different what user specifies in QEMU. > > > If so, we should be able to sanity check the > > use of these features in QEMU for the named CPU models / feature > > selection too. > > This series enhances get_supported_cpuid() for TDX. If named CPU models are > used to boot a TDX guest, it likely gets warning of "xxx feature is not > available" If the ',check=on' arg is given to -cpu, does it ensure that the guest fails to startup with an incompatible feature set ? That's really the key thing to protect the user from mistakes. > We have another series to enhance the "-feature" for TDX, to warn out if > some fixed1 is specified to be removed. Besides, we will introduce specific > named CPU model for TDX. e.g., TDX-SapphireRapids which contains the maximum > feature set a TDX guest can have on SPR host. I don't know if this is the right approach or not, but we should at least consider making use of CPU versioning here. ie have a single "SapphireRapids" alias, which resolves to a suitable specific CPU version depending on whether TDX is used or not. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
