Re: [PATCH v19 083/130] KVM: TDX: Add TSX_CTRL msr into uret_msrs list

Binbin Wu
2024-04-07T07:05:27Z

On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote:
> From: Yang Weijiang <weijiang.yang@intel.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@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.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;
>