[PATCH 6/7] KVM: TDX: restore user ret MSRs

[Adrian Hunter <adrian.hunter@xxxxxxxxx>]

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
treatment, this patch doesn't address it.

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>
---
TD vcpu enter/exit v1:
 - Rename tdx_user_return_update_cache() ->
     tdx_user_return_msr_update_cache() (extrapolated from Binbin)
 - Adjust to rename in previous patches (Binbin)
 - Simplify comment (Tony)
 - Move code change in tdx_hardware_setup() to __tdx_bringup().
---
 arch/x86/kvm/vmx/tdx.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 00fdd2932205..4a33ca54c8ba 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2,7 +2,6 @@
 #include <linux/cleanup.h>
 #include <linux/cpu.h>
 #include <linux/mmu_context.h>
-
 #include <asm/fpu/xcr.h>
 #include <asm/tdx.h>
 #include "capabilities.h"
@@ -711,6 +710,28 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu)
 }
 
 
+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_restore_host_xsave_state(struct kvm_vcpu *vcpu)
 {
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
@@ -796,6 +817,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 
 	tdx_vcpu_enter_exit(vcpu);
 
+	tdx_user_return_msr_update_cache();
 	tdx_restore_host_xsave_state(vcpu);
 	tdx->host_state_need_restore = true;
 
@@ -2233,6 +2255,24 @@ static int __init __tdx_bringup(void)
 	for_each_possible_cpu(i)
 		INIT_LIST_HEAD(&per_cpu(associated_tdvcpus, 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,
 	 * as making SEAMCALLs requires CPU being in post-VMXON state.
-- 
2.43.0