Re: [PATCH] KVM: nVMX: Dynamically compute max VMCS index for vmcs12

[Paolo Bonzini]

On 06/07/21 05:05, Hu, Robert wrote:
> > As noted in the code comments, KVM allows VMREAD/VMWRITE to all defined
> > fields, whether or not the field should actually exist for the vCPU model doesn't
> > enter into the equation.  That's technically wrong as there are a number of
> > fields that the SDM explicitly states exist iff a certain feature is supported.  To
> > fix that we'd need to add a "feature flag" to vmcs_field_to_offset_table that is
> > checked against the vCPU model, though updating the MSR would probably fall
> > onto userspace's shoulders?
>
> [Hu, Robert]
> Perhaps more easier and proper to do this in KVM side.
> QEMU sets actual feature set down to KVM, and KVM updates IA32_VMX_VMCS_ENUM
> MSR accordingly. We don't see a channel that QEMU constructs a VMCS and sets a whole
> to KVM.

Yes, it's possible to do that too.  If that is included in Linux 5.14, 
we can remove it from QEMU.

Paolo