Re: [PATCH v3 09/10] KVM: TDX: Save and restore IA32_DEBUGCTL

[Xiaoyao Li]

On 3/8/2025 5:20 AM, Paolo Bonzini wrote:
> From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>
> Save the IA32_DEBUGCTL MSR before entering a TDX VCPU and restore it
> afterwards.  The TDX Module preserves bits 1, 12, and 14, so if no
> other bits are set, no restore is done.

Reviewed-by: Xiayao Li <xiaoyao.li@xxxxxxxxx>

> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Message-ID: <20250129095902.16391-12-adrian.hunter@xxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>   arch/x86/kvm/vmx/tdx.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 5625b0801ce8..25972e12504b 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -683,6 +683,8 @@ void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>   	else
>   		vt->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
>   
> +	vt->host_debugctlmsr = get_debugctlmsr();
> +
>   	vt->guest_state_loaded = true;
>   }
>   
> @@ -826,11 +828,15 @@ static void tdx_load_host_xsave_state(struct kvm_vcpu *vcpu)
>   	if (kvm_host.xss != (kvm_tdx->xfam & kvm_caps.supported_xss))
>   		wrmsrl(MSR_IA32_XSS, kvm_host.xss);
>   }
> -EXPORT_SYMBOL_GPL(kvm_load_host_xsave_state);

This needs to be cleaned up in patch 05;

> +
> +#define TDX_DEBUGCTL_PRESERVED (DEBUGCTLMSR_BTF | \
> +				DEBUGCTLMSR_FREEZE_PERFMON_ON_PMI | \
> +				DEBUGCTLMSR_FREEZE_IN_SMM)
>   
>   fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
>   {
>   	struct vcpu_tdx *tdx = to_tdx(vcpu);
> +	struct vcpu_vt *vt = to_vt(vcpu);
>   
>   	/*
>   	 * force_immediate_exit requires vCPU entering for events injection with
> @@ -846,6 +852,9 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
>   
>   	tdx_vcpu_enter_exit(vcpu);
>   
> +	if (vt->host_debugctlmsr & ~TDX_DEBUGCTL_PRESERVED)
> +		update_debugctlmsr(vt->host_debugctlmsr);
> +
>   	tdx_load_host_xsave_state(vcpu);
>   	tdx->guest_entered = true;
>