[kvm-unit-tests RFC 14/16] x86 AMD SEV-ES: Copy UEFI #VC IDT entry

[Zixuan Wang <zixuanwang@google.com>]

AMD SEV-ES introduces a new #VC exception that handles the communication
between guest and host.  UEFI already implements a #VC handler so there
is no need to re-implement it in KVM-Unit-Tests. To reuse this #VC
handler, this commit reads UEFI's IDT, copy the #VC IDT entry into
KVM-Unit-Tests' IDT.

In this commit, load_idt() can work and now guest crashes in
setup_page_table(), which will be fixed by follow-up commits.

Signed-off-by: Zixuan Wang <zixuanwang@google.com>
---
 lib/x86/amd_sev.c | 10 ++++++++++
 lib/x86/amd_sev.h |  5 +++++
 2 files changed, 15 insertions(+)

diff --git a/lib/x86/amd_sev.c b/lib/x86/amd_sev.c
index c2aebdf..04b6912 100644
--- a/lib/x86/amd_sev.c
+++ b/lib/x86/amd_sev.c
@@ -46,11 +46,21 @@ EFI_STATUS setup_amd_sev(void)
 
 #ifdef CONFIG_AMD_SEV_ES
 EFI_STATUS setup_amd_sev_es(void){
+	struct descriptor_table_ptr idtr;
+	idt_entry_t *idt;
+
 	/* Test if SEV-ES is enabled */
 	if (!(rdmsr(MSR_SEV_STATUS) & SEV_ES_ENABLED_MASK)) {
 		return EFI_UNSUPPORTED;
 	}
 
+	/* Copy UEFI's #VC IDT entry, so KVM-Unit-Tests can reuse it and does
+	 * not have to re-implement a #VC handler
+	 */
+	sidt(&idtr);
+	idt = (idt_entry_t *)idtr.base;
+	boot_idt[SEV_ES_VC_HANDLER_VECTOR] = idt[SEV_ES_VC_HANDLER_VECTOR];
+
 	return EFI_SUCCESS;
 }
 
diff --git a/lib/x86/amd_sev.h b/lib/x86/amd_sev.h
index 4d81cae..5ebd4a6 100644
--- a/lib/x86/amd_sev.h
+++ b/lib/x86/amd_sev.h
@@ -36,6 +36,11 @@
 #define SEV_ENABLED_MASK    0b1
 #define SEV_ES_ENABLED_MASK 0b10
 
+/* AMD Programmer's Manual Volume 2
+ *   - Section "#VC Exception"
+ */
+#define SEV_ES_VC_HANDLER_VECTOR 29
+
 EFI_STATUS setup_amd_sev(void);
 #ifdef CONFIG_AMD_SEV_ES
 EFI_STATUS setup_amd_sev_es(void);
-- 
2.33.0.rc1.237.g0d66db33f3-goog