x86/sev-es: Support CPU offline/online

Add a play_dead handler when running under SEV-ES. This is needed
because the hypervisor can't deliver an SIPI request to restart the AP.
Instead, the kernel has to issue a VMGEXIT to halt the VCPU until the
hypervisor wakes it up again.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-70-joro@8bytes.org

arch/x86/include/uapi/asm/svm.h

@@ -84,6 +84,7 @@
 /* SEV-ES software-defined VMGEXIT events */
 #define SVM_VMGEXIT_MMIO_READ			0x80000001
 #define SVM_VMGEXIT_MMIO_WRITE			0x80000002
+#define SVM_VMGEXIT_AP_HLT_LOOP			0x80000004
 #define SVM_VMGEXIT_AP_JUMP_TABLE		0x80000005
 #define SVM_VMGEXIT_SET_AP_JUMP_TABLE		0
 #define SVM_VMGEXIT_GET_AP_JUMP_TABLE		1

arch/x86/kernel/sev-es.c

@@ -29,6 +29,8 @@
 #include <asm/realmode.h>
 #include <asm/traps.h>
 #include <asm/svm.h>
+#include <asm/smp.h>
+#include <asm/cpu.h>
 
 #define DR7_RESET_VALUE        0x400
 
@@ -518,6 +520,65 @@ static bool __init sev_es_setup_ghcb(void)
 	return true;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static void sev_es_ap_hlt_loop(void)
+{
+	struct ghcb_state state;
+	struct ghcb *ghcb;
+
+	ghcb = sev_es_get_ghcb(&state);
+
+	while (true) {
+		vc_ghcb_invalidate(ghcb);
+		ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_AP_HLT_LOOP);
+		ghcb_set_sw_exit_info_1(ghcb, 0);
+		ghcb_set_sw_exit_info_2(ghcb, 0);
+
+		sev_es_wr_ghcb_msr(__pa(ghcb));
+		VMGEXIT();
+
+		/* Wakeup signal? */
+		if (ghcb_sw_exit_info_2_is_valid(ghcb) &&
+		    ghcb->save.sw_exit_info_2)
+			break;
+	}
+
+	sev_es_put_ghcb(&state);
+}
+
+/*
+ * Play_dead handler when running under SEV-ES. This is needed because
+ * the hypervisor can't deliver an SIPI request to restart the AP.
+ * Instead the kernel has to issue a VMGEXIT to halt the VCPU until the
+ * hypervisor wakes it up again.
+ */
+static void sev_es_play_dead(void)
+{
+	play_dead_common();
+
+	/* IRQs now disabled */
+
+	sev_es_ap_hlt_loop();
+
+	/*
+	 * If we get here, the VCPU was woken up again. Jump to CPU
+	 * startup code to get it back online.
+	 */
+	start_cpu0();
+}
+#else  /* CONFIG_HOTPLUG_CPU */
+#define sev_es_play_dead	native_play_dead
+#endif /* CONFIG_HOTPLUG_CPU */
+
+#ifdef CONFIG_SMP
+static void __init sev_es_setup_play_dead(void)
+{
+	smp_ops.play_dead = sev_es_play_dead;
+}
+#else
+static inline void sev_es_setup_play_dead(void) { }
+#endif
+
 static void __init alloc_runtime_data(int cpu)
 {
 	struct sev_es_runtime_data *data;
@@ -566,6 +627,8 @@ void __init sev_es_init_vc_handling(void)
 		setup_vc_stacks(cpu);
 	}
 
+	sev_es_setup_play_dead();
+
 	/* Secondary CPUs use the runtime #VC handler */
 	initial_vc_handler = (unsigned long)safe_stack_exc_vmm_communication;
 }