linux-kernel - Re: [PATCH v19 082/130] KVM: TDX: restore user ret MSRs

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Date: Sun, 7 Apr 2024 13:59:03 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v19 082/130] KVM: TDX: restore user ret MSRs



On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> Several user ret MSRs are clobbered on TD exit.  Restore those values on
> TD exit

Here "Restore" is not accurate, since the previous patch just updates 
the cached value on TD exit.

> and before returning to ring 3.  Because TSX_CTRL requires special
> treat, this patch doesn't address it.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   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 199226c6cf55..7e2b1e554246 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -535,6 +535,28 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	 */
>   }
>   
> +struct tdx_uret_msr {
> +	u32 msr;
> +	unsigned int slot;
> +	u64 defval;
> +};
> +
> +static struct tdx_uret_msr tdx_uret_msrs[] = {
> +	{.msr = MSR_SYSCALL_MASK, .defval = 0x20200 },
> +	{.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);
> @@ -627,6 +649,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
>   
>   	tdx_vcpu_enter_exit(tdx);
>   
> +	tdx_user_return_update_cache();
>   	tdx_restore_host_xsave_state(vcpu);
>   	tdx->host_state_need_restore = true;
>   
> @@ -1972,6 +1995,26 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>   		return -EINVAL;
>   	}
>   
> +	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().
Should be tdx_user_return_update_cache(), if it's the final API name.

> +		 * Here is setting up cpu feature before running vcpu,
> +		 * registered is already false.
                                   ^
                            remove "already"?

> +		 */
> +		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);