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

Binbin Wu
2024-04-07T05:59:08Z

On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.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@intel.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.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);