Re: [PATCH v19 024/130] KVM: TDX: Add placeholders for TDX VM/vcpu structure

Huang, Kai
2024-04-23T13:59:10Z

On Fri, 2024-03-22 at 15:45 -0700, Isaku Yamahata wrote:
> Hmm, now I noticed the vm_size can be moved here.  We have
>
>   vcpu_size = sizeof(struct vcpu_vmx);
>   vcpu_align = __alignof__(struct vcpu_vmx);
> if (enable_tdx) {
> vcpu_size = max_t(unsigned int, vcpu_size,
>   sizeof(struct vcpu_tdx));
> vcpu_align = max_t(unsigned int, vcpu_align,
>    __alignof__(struct vcpu_tdx));
>                 vt_x86_ops.vm_size = max_t(unsigned int, vt_x86_ops.vm_size,
>                                           sizeof(struct kvm_tdx));
> }

Hmm.. After reading again, I don't think we can?

In your comments that was replied to Binbin:

/*
* vt_hardware_setup() updates vt_x86_ops. Because kvm_ops_update()
* copies vt_x86_ops to kvm_x86_op, vt_x86_ops must be updated before
* kvm_ops_update() called by kvm_x86_vendor_init().
*/

You said update to vt_x86_ops.vm_size must be done in vt_hardware_setup().

But I think we should move the above comment to the vt_hardware_setup()
where vm_size is truly updated.

/*
* TDX and VMX have different VM structure. If TDX is enabled,
* update vt_x86_ops.vm_size to the maximum value of the two
* before it is copied to kvm_x86_ops in kvm_update_ops() to make
* sure KVM always allocates enough memory for the VM structure.
*/

Here the purpose to calculate vcpu_size/vcpu_align is just to pass them to
kvm_init(). If needed, we can add a comment to describe "what this code
does":

/*
* TDX and VMX have different vCPU structure. Calculate the
* maximum size/align so that kvm_init() can use the larger
* values to create the vCPU kmem_cache.
*/