[PATCH 6/7] x86/sev: Register the guest with the SVSM APIC protocol

[Melody Wang]

The SVSM APIC protocol supports 5 calls. SVSM_APIC_CONFIGURE_EMULATION
(shortened to SVSM_APIC_CONFIG_EMULATION for brevity), call 1, provides
the controls whether the guest can make use of the SVSM APIC protocol.

Implement this call, and register Alternate Injection for the guest
by default.

Signed-off-by: Melody Wang <huibo.wang@xxxxxxx>
---
 arch/x86/boot/compressed/sev.c | 17 +++++++++++++++++
 arch/x86/boot/compressed/sev.h |  6 ++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 655291a03dcc..a98185b3869a 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -518,5 +518,22 @@ u64 sev_prepare(void)
 	if (unsupported)
 		return unsupported;
 
+	/* Register Alternate Injection */
+	if (early_is_sevsnp_guest() && snp_vmpl) {
+		struct svsm_call call = {};
+		int ret;
+
+		if (!(sev_get_status() & MSR_AMD64_SNP_ALTERNATE_INJ))
+			return 0;
+
+		call.caa = (struct svsm_ca *)boot_svsm_caa_pa;
+		call.rax = SVSM_APIC_CALL(SVSM_APIC_CONFIG_EMULATION);
+		call.rcx = SVSM_AI_REGISTER;
+
+		ret = svsm_call_msr_protocol(&call);
+		if (ret)
+			sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
+	}
+
 	return 0;
 }
diff --git a/arch/x86/boot/compressed/sev.h b/arch/x86/boot/compressed/sev.h
index 22637b416b46..dd058af2e7aa 100644
--- a/arch/x86/boot/compressed/sev.h
+++ b/arch/x86/boot/compressed/sev.h
@@ -12,6 +12,12 @@
 
 #include <asm/shared/msr.h>
 
+enum svsm_ai_ctrl {
+	SVSM_AI_DISABLE,
+	SVSM_AI_DEREGISTER,
+	SVSM_AI_REGISTER,
+};
+
 void snp_accept_memory(phys_addr_t start, phys_addr_t end);
 u64 sev_get_status(void);
 bool early_is_sevsnp_guest(void);
-- 
2.43.0