[PATCH v3 07/10] KVM: TDX: restore user ret MSRs

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Several user ret MSRs are clobbered on TD exit.  Ensure the MSR cache is
updated on vcpu_put, and the MSRs themselves before returning to ring 3.

Co-developed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
Signed-off-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Message-ID: <20250129095902.16391-10-adrian.hunter@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/tdx.c | 51 +++++++++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/vmx/tdx.h |  1 +
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index b2948318cd8b..5819ed926166 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -646,9 +646,32 @@ void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	vt->guest_state_loaded = true;
 }
 
+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_msr_update_cache(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
+		kvm_user_return_msr_update_cache(tdx_uret_msrs[i].slot,
+						 tdx_uret_msrs[i].defval);
+}
+
 static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vt *vt = to_vt(vcpu);
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
 
 	if (!vt->guest_state_loaded)
 		return;
@@ -656,6 +679,11 @@ static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
 	++vcpu->stat.host_state_reload;
 	wrmsrl(MSR_KERNEL_GS_BASE, vt->msr_host_kernel_gs_base);
 
+	if (tdx->guest_entered) {
+		tdx_user_return_msr_update_cache();
+		tdx->guest_entered = false;
+	}
+
 	vt->guest_state_loaded = false;
 }
 
@@ -762,6 +790,8 @@ EXPORT_SYMBOL_GPL(kvm_load_host_xsave_state);
 
 fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 {
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+
 	/*
 	 * force_immediate_exit requires vCPU entering for events injection with
 	 * an immediately exit followed. But The TDX module doesn't guarantee
@@ -777,6 +807,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 	tdx_vcpu_enter_exit(vcpu);
 
 	tdx_load_host_xsave_state(vcpu);
+	tdx->guest_entered = true;
 
 	vcpu->arch.regs_avail &= TDX_REGS_AVAIL_SET;
 
@@ -2236,7 +2267,25 @@ static int __init __do_tdx_bringup(void)
 static int __init __tdx_bringup(void)
 {
 	const struct tdx_sys_info_td_conf *td_conf;
-	int r;
+	int r, i;
+
+	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
+		/*
+		 * Check 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
+		 * tdx_user_return_msr_update_cache().
+		 */
+		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;
+		}
+	}
 
 	/*
 	 * Enabling TDX requires enabling hardware virtualization first,
diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
index 6eb24bbacccc..55af3d866ff6 100644
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -56,6 +56,7 @@ struct vcpu_tdx {
 	u64 vp_enter_ret;
 
 	enum vcpu_tdx_state state;
+	bool guest_entered;
 };
 
 void tdh_vp_rd_failed(struct vcpu_tdx *tdx, char *uclass, u32 field, u64 err);
-- 
2.43.5