Re: [PATCH v10 072/108] KVM: TDX: restore user ret MSRs

[Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>]

On 10/30/2022 2:23 PM, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>
> Several user ret MSRs are clobbered on TD exit.  Restore those values on
> TD exit and before returning to ring 3.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>   arch/x86/kvm/vmx/tdx.c | 43 ++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 43 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 3ec465cbaeef..f35ccf2b502d 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -456,6 +456,28 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	vcpu->kvm->vm_bugged = true;
>   }
>   
> +struct tdx_uret_msr {
> +	u32 msr;
> +	unsigned int slot;
> +	u64 defval;
> +};
> +
> +static struct tdx_uret_msr tdx_uret_msrs[] = {
> +	{.msr = MSR_SYSCALL_MASK,},
> +	{.msr = MSR_STAR,},
> +	{.msr = MSR_LSTAR,},
> +	{.msr = MSR_TSC_AUX,},
> +};
> +
> +static void tdx_user_return_update_cache(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
> +		kvm_user_return_update_cache(tdx_uret_msrs[i].slot,
> +					     tdx_uret_msrs[i].defval);
> +}
> +
>   static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> @@ -495,6 +517,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
>   
>   	tdx_vcpu_enter_exit(vcpu, tdx);
>   
> +	tdx_user_return_update_cache();
>   	tdx_restore_host_xsave_state(vcpu);
>   	tdx->host_state_need_restore = true;
>   
> @@ -1558,6 +1581,26 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>   		return -ENODEV;
>   	}
>   
> +	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
> +		/*
> +		 * Here it checks if MSRs (tdx_uret_msrs) can be saved/restored
> +		 * before returning to user space.
> +		 *
> +		 * this_cpu_ptr(user_return_msrs)->registered isn't checked
> +		 * because the registration is done at vcpu runtime by
> +		 * kvm_set_user_return_msr().
> +		 * Here is setting up cpu feature before running vcpu,
> +		 * registered is alreays

typo, already or always?



>   false.
> +		 */
> +		tdx_uret_msrs[i].slot = kvm_find_user_return_msr(tdx_uret_msrs[i].msr);
> +		if (tdx_uret_msrs[i].slot == -1) {
> +			/* If any MSR isn't supported, it is a KVM bug */
> +			pr_err("MSR %x isn't included by kvm_find_user_return_msr\n",
> +				tdx_uret_msrs[i].msr);
> +			return -EIO;
> +		}
> +	}
> +
>   	max_pkgs = topology_max_packages();
>   	tdx_mng_key_config_lock = kcalloc(max_pkgs, sizeof(*tdx_mng_key_config_lock),
>   				   GFP_KERNEL);