sev/i386: Don't allow a system reset under an SEV-ES guest

An SEV-ES guest does not allow register state to be altered once it has
been measured. When an SEV-ES guest issues a reboot command, Qemu will
reset the vCPU state and resume the guest. This will cause failures under
SEV-ES. Prevent that from occuring by introducing an arch-specific
callback that returns a boolean indicating whether vCPUs are resettable.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: David Hildenbrand <david@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>
Message-Id: <1ac39c441b9a3e970e9556e1cc29d0a0814de6fd.1611682609.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -2312,6 +2312,11 @@ void kvm_flush_coalesced_mmio_buffer(void)
     s->coalesced_flush_in_progress = false;
 }
 
+bool kvm_cpu_check_are_resettable(void)
+{
+    return kvm_arch_cpu_check_are_resettable();
+}
+
 static void do_kvm_cpu_synchronize_state(CPUState *cpu, run_on_cpu_data arg)
 {
     if (!cpu->vcpu_dirty) {

include/sysemu/cpus.h

@@ -41,6 +41,8 @@ extern int icount_align_option;
 /* Unblock cpu */
 void qemu_cpu_kick_self(void);
 
+bool cpus_are_resettable(void);
+
 void cpu_synchronize_all_states(void);
 void cpu_synchronize_all_post_reset(void);
 void cpu_synchronize_all_post_init(void);

include/sysemu/hw_accel.h

@@ -22,4 +22,9 @@ void cpu_synchronize_post_reset(CPUState *cpu);
 void cpu_synchronize_post_init(CPUState *cpu);
 void cpu_synchronize_pre_loadvm(CPUState *cpu);
 
+static inline bool cpu_check_are_resettable(void)
+{
+    return kvm_enabled() ? kvm_cpu_check_are_resettable() : true;
+}
+
 #endif /* QEMU_HW_ACCEL_H */

include/sysemu/kvm.h

@@ -541,4 +541,14 @@ int kvm_get_max_memslots(void);
 /* Notify resamplefd for EOI of specific interrupts. */
 void kvm_resample_fd_notify(int gsi);
 
+/**
+ * kvm_cpu_check_are_resettable - return whether CPUs can be reset
+ *
+ * Returns: true: CPUs are resettable
+ *          false: CPUs are not resettable
+ */
+bool kvm_cpu_check_are_resettable(void);
+
+bool kvm_arch_cpu_check_are_resettable(void);
+
 #endif

softmmu/cpus.c

@@ -194,6 +194,11 @@ void cpu_synchronize_pre_loadvm(CPUState *cpu)
     }
 }
 
+bool cpus_are_resettable(void)
+{
+    return cpu_check_are_resettable();
+}
+
 int64_t cpus_get_virtual_clock(void)
 {
     /*

softmmu/runstate.c

@@ -528,6 +528,9 @@ void qemu_system_reset_request(ShutdownCause reason)
     if (reboot_action == REBOOT_ACTION_SHUTDOWN &&
         reason != SHUTDOWN_CAUSE_SUBSYSTEM_RESET) {
         shutdown_requested = reason;
+    } else if (!cpus_are_resettable()) {
+        error_report("cpus are not resettable, terminating");
+        shutdown_requested = reason;
     } else {
         reset_requested = reason;
     }

target/arm/kvm.c

@@ -1045,3 +1045,8 @@ int kvm_arch_msi_data_to_gsi(uint32_t data)
 {
     return (data - 32) & 0xffff;
 }
+
+bool kvm_arch_cpu_check_are_resettable(void)
+{
+    return true;
+}

target/i386/kvm/kvm.c

@@ -27,6 +27,7 @@
 #include "sysemu/kvm_int.h"
 #include "sysemu/runstate.h"
 #include "kvm_i386.h"
+#include "sev_i386.h"
 #include "hyperv.h"
 #include "hyperv-proto.h"
 
@@ -4821,3 +4822,8 @@ bool kvm_has_waitpkg(void)
 {
     return has_msr_umwait;
 }
+
+bool kvm_arch_cpu_check_are_resettable(void)
+{
+    return !sev_es_enabled();
+}

target/mips/kvm.c

@@ -1290,3 +1290,8 @@ int mips_kvm_type(MachineState *machine, const char *vm_type)
 
     return -1;
 }
+
+bool kvm_arch_cpu_check_are_resettable(void)
+{
+    return true;
+}

target/ppc/kvm.c

@@ -2929,3 +2929,8 @@ void kvmppc_set_reg_tb_offset(PowerPCCPU *cpu, int64_t tb_offset)
         kvm_set_one_reg(cs, KVM_REG_PPC_TB_OFFSET, &tb_offset);
     }
 }
+
+bool kvm_arch_cpu_check_are_resettable(void)
+{
+    return true;
+}

target/s390x/kvm.c

@@ -2599,3 +2599,8 @@ void kvm_s390_stop_interrupt(S390CPU *cpu)
 
     kvm_s390_vcpu_interrupt(cpu, &irq);
 }
+
+bool kvm_arch_cpu_check_are_resettable(void)
+{
+    return true;
+}