[PATCH v4 73/75] x86/sev-es: Handle NMI State

Joerg Roedel
Tue, 14 Jul 2020 12:09:15 -0000

When running under SEV-ES the kernel has to tell the hypervisor when to
open the NMI window again after an NMI was injected. This is done with
an NMI-complete message to the hypervisor.

Add code to the kernels NMI handler to send this message right at the
beginning of do_nmi(). This always allows nesting NMIs.

Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 arch/x86/include/asm/sev-es.h   |  2 ++
 arch/x86/include/uapi/asm/svm.h |  1 +
 arch/x86/kernel/nmi.c           |  6 ++++++
 arch/x86/kernel/sev-es.c        | 21 +++++++++++++++++++++
 4 files changed, 30 insertions(+)

diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 25ab44f977db..de4d3f63fdf8 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -84,10 +84,12 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 extern void sev_es_ist_enter(struct pt_regs *regs);
 extern void sev_es_ist_exit(void);
 extern int sev_es_setup_ap_jump_table(struct real_mode_header *rmh);
+extern void sev_es_nmi_complete(void);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
 static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) {
return 0; }
+static inline void sev_es_nmi_complete(void) { }
 #endif

 #endif
diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
index 20a05839dd9a..0f837339db66 100644
--- a/arch/x86/include/uapi/asm/svm.h
+++ b/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_NMI_COMPLETE		0x80000003
 #define SVM_VMGEXIT_AP_HLT_LOOP			0x80000004
 #define SVM_VMGEXIT_AP_JUMP_TABLE		0x80000005
 #define		SVM_VMGEXIT_SET_AP_JUMP_TABLE			0
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index d94a5bb0bebc..2d60220bf6d5 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -479,6 +479,12 @@ static DEFINE_PER_CPU(unsigned long, nmi_dr7);

 DEFINE_IDTENTRY_RAW(exc_nmi)
 {
+	/*
+	 * Re-enable NMIs right here when running as an SEV-ES guest. This might
+	 * cause nested NMIs, but those can be handled safely.
+	 */
+	sev_es_nmi_complete();
+
 	if (IS_ENABLED(CONFIG_SMP) && arch_cpu_is_offline(smp_processor_id()))
 		return;

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index b147d97856c3..ff440b6e5e78 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -423,6 +423,27 @@ static bool vc_slow_virt_to_phys(struct ghcb *ghcb, struct
es_em_ctxt *ctxt,
 /* Include code shared with pre-decompression boot stage */
 #include "sev-es-shared.c"

+void sev_es_nmi_complete(void)
+{
+	struct ghcb_state state;
+	struct ghcb *ghcb;
+
+	if (!sev_es_active())
+		return;
+
+	ghcb = sev_es_get_ghcb(&state);
+
+	vc_ghcb_invalidate(ghcb);
+	ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_NMI_COMPLETE);
+	ghcb_set_sw_exit_info_1(ghcb, 0);
+	ghcb_set_sw_exit_info_2(ghcb, 0);
+
+	sev_es_wr_ghcb_msr(__pa(ghcb));
+	VMGEXIT();
+
+	sev_es_put_ghcb(&state);
+}
+
 static u64 sev_es_get_jump_table_addr(void)
 {
 	struct ghcb_state state;
--
2.27.0