[PATCH v6 74/76] x86/sev-es: Handle NMI State

Joerg Roedel
2020-08-24T09:07:18Z

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>
Link: https://lore.kernel.org/r/20200724160336.5435-74-joro@8bytes.org
---
arch/x86/include/asm/sev-es.h | 7 +++++++
arch/x86/include/uapi/asm/svm.h | 1 +
arch/x86/kernel/nmi.c | 6 ++++++
arch/x86/kernel/sev-es.c | 18 ++++++++++++++++++
4 files changed, 32 insertions(+)

diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 6ca38dc378e0..21fdee11ac83 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -95,10 +95,17 @@ static __always_inline void sev_es_ist_exit(void)
__sev_es_ist_exit();
}
extern int sev_es_setup_ap_jump_table(struct real_mode_header *rmh);
+extern void __sev_es_nmi_complete(void);
+static __always_inline void sev_es_nmi_complete(void)
+{
+ if (static_branch_unlikely(&sev_es_enable_key))
+ __sev_es_nmi_complete();
+}
#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 951f098a4bf5..16ce58c7ed0f 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -478,6 +478,12 @@ DEFINE_IDTENTRY_RAW(exc_nmi)
{
bool irq_state;

+ /*
+ * 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 597ebb73411f..7202d2f5deb8 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -414,6 +414,24 @@ 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;
+
+ 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;