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

Joerg Roedel
2020-04-28T15:18:28Z

From: Joerg Roedel <jroedel@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@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