linux-kernel - Re: [PATCH v19 083/130] KVM: TDX: Add TSX_CTRL msr into uret

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Message-ID: <dec685d5-96a7-453d-8b1b-7c662e222977@linux.intel.com>
Date: Sun, 7 Apr 2024 15:05:21 +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,
 Yang Weijiang <weijiang.yang@...el.com>
Subject: Re: [PATCH v19 083/130] KVM: TDX: Add TSX_CTRL msr into uret_msrs
 list



On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> From: Yang Weijiang <weijiang.yang@...el.com>
>
> TDX module resets the TSX_CTRL MSR to 0 at TD exit if TSX is enabled for
> TD. Or it preserves the TSX_CTRL MSR if TSX is disabled for TD.  VMM can
> rely on uret_msrs mechanism to defer the reload of host value until exiting
> to user space.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> v19:
> - fix the type of tdx_uret_tsx_ctrl_slot. unguent int => int.
> ---
>   arch/x86/kvm/vmx/tdx.c | 33 +++++++++++++++++++++++++++++++--
>   arch/x86/kvm/vmx/tdx.h |  8 ++++++++
>   2 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 7e2b1e554246..83dcaf5b6fbd 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -547,14 +547,21 @@ static struct tdx_uret_msr tdx_uret_msrs[] = {
>   	{.msr = MSR_LSTAR,},
>   	{.msr = MSR_TSC_AUX,},
>   };
> +static int tdx_uret_tsx_ctrl_slot;
>   
> -static void tdx_user_return_update_cache(void)
> +static void tdx_user_return_update_cache(struct kvm_vcpu *vcpu)
>   {
>   	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);
> +	/*
> +	 * TSX_CTRL is reset to 0 if guest TSX is supported. Otherwise
> +	 * preserved.
> +	 */
> +	if (to_kvm_tdx(vcpu->kvm)->tsx_supported && tdx_uret_tsx_ctrl_slot != -1)

If to_kvm_tdx(vcpu->kvm)->tsx_supported is true, tdx_uret_tsx_ctrl_slot 
shouldn't be -1 at this point.
Otherwise, it's a KVM bug, right?
Not sure if it needs a warning if tdx_uret_tsx_ctrl_slot is -1, or just 
remove the check?

> +		kvm_user_return_update_cache(tdx_uret_tsx_ctrl_slot, 0);
>   }
>   
>   static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
> @@ -649,7 +656,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
>   
>   	tdx_vcpu_enter_exit(tdx);
>   
> -	tdx_user_return_update_cache();
> +	tdx_user_return_update_cache(vcpu);
>   	tdx_restore_host_xsave_state(vcpu);
>   	tdx->host_state_need_restore = true;
>   
> @@ -1167,6 +1174,22 @@ static int setup_tdparams_xfam(struct kvm_cpuid2 *cpuid, struct td_params *td_pa
>   	return 0;
>   }
>   
> +static bool tdparams_tsx_supported(struct kvm_cpuid2 *cpuid)
> +{
> +	const struct kvm_cpuid_entry2 *entry;
> +	u64 mask;
> +	u32 ebx;
> +
> +	entry = kvm_find_cpuid_entry2(cpuid->entries, cpuid->nent, 0x7, 0);
> +	if (entry)
> +		ebx = entry->ebx;
> +	else
> +		ebx = 0;
> +
> +	mask = __feature_bit(X86_FEATURE_HLE) | __feature_bit(X86_FEATURE_RTM);
> +	return ebx & mask;
> +}
> +
>   static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
>   			struct kvm_tdx_init_vm *init_vm)
>   {
> @@ -1209,6 +1232,7 @@ static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
>   	MEMCPY_SAME_SIZE(td_params->mrowner, init_vm->mrowner);
>   	MEMCPY_SAME_SIZE(td_params->mrownerconfig, init_vm->mrownerconfig);
>   
> +	to_kvm_tdx(kvm)->tsx_supported = tdparams_tsx_supported(cpuid);
>   	return 0;
>   }
>   
> @@ -2014,6 +2038,11 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>   			return -EIO;
>   		}
>   	}
> +	tdx_uret_tsx_ctrl_slot = kvm_find_user_return_msr(MSR_IA32_TSX_CTRL);
> +	if (tdx_uret_tsx_ctrl_slot == -1 && boot_cpu_has(X86_FEATURE_MSR_TSX_CTRL)) {
> +		pr_err("MSR_IA32_TSX_CTRL isn't included by kvm_find_user_return_msr\n");
> +		return -EIO;
> +	}
>   
>   	max_pkgs = topology_max_packages();
>   	tdx_mng_key_config_lock = kcalloc(max_pkgs, sizeof(*tdx_mng_key_config_lock),
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index e96c416e73bf..44eab734e702 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -17,6 +17,14 @@ struct kvm_tdx {
>   	u64 xfam;
>   	int hkid;
>   
> +	/*
> +	 * Used on each TD-exit, see tdx_user_return_update_cache().
> +	 * TSX_CTRL value on TD exit
> +	 * - set 0     if guest TSX enabled
> +	 * - preserved if guest TSX disabled
> +	 */
> +	bool tsx_supported;
> +
>   	bool finalized;
>   	atomic_t tdh_mem_track;
>