[PATCH v7 068/102] KVM: TDX: restore user ret MSRs

isaku.yamahata
2022-06-27T21:57:40Z

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