x86/sev-es: Handle NMI State

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 kernel's NMI handler to send this message right at the
beginning of do_nmi(). This always allows nesting NMIs.

 [ bp: Mark __sev_es_nmi_complete() noinstr:
   vmlinux.o: warning: objtool: exc_nmi()+0x17: call to __sev_es_nmi_complete()
	leaves .noinstr.text section
   While at it, use __pa_nodebug() for the same reason due to
   CONFIG_DEBUG_VIRTUAL=y:
   vmlinux.o: warning: objtool: __sev_es_nmi_complete()+0xd9: call to __phys_addr()
   	leaves .noinstr.text section ]

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-71-joro@8bytes.org

2 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 4c89c4d3cb82..56b64d779856 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 d1bcd0dca583..b6518e96dedb 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -408,6 +408,24 @@ 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 noinstr __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_nodebug(ghcb));
+	VMGEXIT();
+
+	sev_es_put_ghcb(&state);
+}
+
 static u64 get_jump_table_addr(void)
 {
 	struct ghcb_state state;