Re: [PATCH V2 05/12] KVM: TDX: Implement TDX vcpu enter/exit path

Xiaoyao Li
2025-02-20T13:16:10Z

On 1/29/2025 5:58 PM, Adrian Hunter wrote:
> +#define TDX_REGS_UNSUPPORTED_SET (BIT(VCPU_EXREG_RFLAGS) | \
> + BIT(VCPU_EXREG_SEGMENTS))
> +
> +fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
> +{
> + /*
> + * force_immediate_exit requires vCPU entering for events injection with
> + * an immediately exit followed. But The TDX module doesn't guarantee
> + * entry, it's already possible for KVM to_think_ it completely entry
> + * to the guest without actually having done so.
> + * Since KVM never needs to force an immediate exit for TDX, and can't
> + * do direct injection, just warn on force_immediate_exit.
> + */
> + WARN_ON_ONCE(force_immediate_exit);
> +
> + trace_kvm_entry(vcpu, force_immediate_exit);
> +
> + tdx_vcpu_enter_exit(vcpu);
> +
> + vcpu->arch.regs_avail &= ~TDX_REGS_UNSUPPORTED_SET;

I don't understand this. Why only clear RFLAGS and SEGMENTS?

When creating the vcpu, vcpu->arch.regs_avail = ~0 in
kvm_arch_vcpu_create().

now it only clears RFLAGS and SEGMENTS for TDX vcpu, which leaves other
bits set. But I don't see any code that syncs the guest value of into
vcpu->arch.regs[reg].

> + trace_kvm_exit(vcpu, KVM_ISA_VMX);
> +
> + return EXIT_FASTPATH_NONE;
> +}