Re: [PATCH v19 104/130] KVM: TDX: Add a place holder for handler of TDX hypercalls (TDG.VP.VMCALL)

[Isaku Yamahata]

On Mon, Apr 01, 2024 at 05:59:35PM +0800,
Chao Gao <chao.gao@xxxxxxxxx> wrote:

> > static inline bool is_td_vcpu_created(struct vcpu_tdx *tdx)
> > {
> > 	return tdx->td_vcpu_created;
> >@@ -897,6 +932,11 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
> > 
> > 	tdx_complete_interrupts(vcpu);
> > 
> >+	if (tdx->exit_reason.basic == EXIT_REASON_TDCALL)
> >+		tdx->tdvmcall.rcx = vcpu->arch.regs[VCPU_REGS_RCX];
> 
> kvm_rcx_read()?
> 
> 		
> >+	else
> >+		tdx->tdvmcall.rcx = 0;
> 
> RCX on TDVMCALL exit is supposed to be consumed by TDX module. I don't get why
> caching it is necessary. Can tdx->tdvmcall be simply dropped?

Now it's not used. Will drop tdvmcall.

It was originally used to remember a original register mask of TDVMCALL, and
tdx_complete_vp_vmcall() used it as a valid value to copy back the output
values.  The current tdx_complete_vp_vmcall() uses kvm_rcx_read() because even
if the user space changes rcx, it doesn't harm to KVM.  KVM does what the user
space tells.
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>