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From:   isaku.yamahata@intel.com
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH v7 068/102] KVM: TDX: restore user ret MSRs
Date:   Mon, 27 Jun 2022 14:54:00 -0700
Message-Id: <e85819d4e4d3a95d709ec132dfbbe310ad73f685.1656366338.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

Several user ret MSRs are clobbered on TD exit.  Restore those values on
TD exit and before returning to ring 3.

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 277525b6ca51..3d9898b677bc 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -593,6 +593,28 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vcpu->kvm->vm_bugged = true;
 }
 
+struct tdx_uret_msr {
+	u32 msr;
+	unsigned int slot;
+	u64 defval;
+};
+
+static struct tdx_uret_msr tdx_uret_msrs[] = {
+	{.msr = MSR_SYSCALL_MASK,},
+	{.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);
@@ -632,6 +654,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
 
 	tdx_vcpu_enter_exit(vcpu, tdx);
 
+	tdx_user_return_update_cache();
 	tdx_restore_host_xsave_state(vcpu);
 	tdx->host_state_need_restore = true;
 
@@ -1470,6 +1493,26 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
 	if (WARN_ON_ONCE(x86_ops->tlb_remote_flush))
 		return -EIO;
 
+	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)->registerd isn't checked
+		 * because the registration is done at vcpu runtime by
+		 * kvm_set_user_return_msr().
+		 * Here is setting up cpu feature before running vcpu,
+		 * registered is alreays 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);
-- 
2.25.1