Re: [PATCH v18 071/121] KVM: TDX: restore user ret MSRs

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On 1/23/2024 7:53 AM, 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.  Because TSX_CTRL requires special
treat, this patch doesn't address it.

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 fe818cfde9e7..4685ff6aa5f8 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -585,6 +585,28 @@ 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);
@@ -677,6 +699,7 @@ 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;
@@ -1936,6 +1959,26 @@ 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().

For tdx, it's done by kvm_user_return_update_cache(), right?

+		 * Here is setting up cpu feature before running vcpu,
+		 * registered is already 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);





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