[PATCH v3 74/75] x86/sev-es: Handle NMI State

Joerg Roedel
Tue, 28 Apr 2020 15:17:24 -0000

From: Joerg Roedel <jroedel at suse.de>

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           |  7 +++++++
 arch/x86/kernel/sev-es.c        | 18 ++++++++++++++++++
 4 files changed, 28 insertions(+)

diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index c89b6e2e6439..a242d16727f1 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -86,6 +86,7 @@ const char *vc_stack_name(enum stack_type type);
 void sev_es_nmi_enter(void);
 void sev_es_nmi_exit(void);
 int sev_es_setup_ap_jump_table(struct real_mode_header *rmh);
+void sev_es_nmi_complete(void);
 #else /* CONFIG_AMD_MEM_ENCRYPT */
 static inline const char *vc_stack_name(enum stack_type type)
 {
@@ -95,6 +96,7 @@ 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 /* CONFIG_AMD_MEM_ENCRYPT*/

 #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 27d1016ec840..8898002e5600 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -511,6 +511,13 @@ NOKPROBE_SYMBOL(is_debug_stack);
 dotraplinkage notrace void
 do_nmi(struct pt_regs *regs, long error_code)
 {
+	/*
+	 * Re-enable NMIs right here when running as an SEV-ES guest. This might
+	 * cause nested NMIs, but those can be handled safely.
+	 */
+	if (sev_es_active())
+		sev_es_nmi_complete();
+
 	if (IS_ENABLED(CONFIG_SMP) && cpu_is_offline(smp_processor_id()))
 		return;

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 00a5d0483730..eef6e2196ef4 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -341,6 +341,24 @@ static phys_addr_t vc_slow_virt_to_phys(struct ghcb *ghcb,
unsigned long vaddr)
 /* 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;
+
+	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;
--
2.17.1