[RFC kvm-unit-tests 05/12] x86: AMD SEV-ES: Prepare for #VC processing

[Varad Gautam <varadgautam@gmail.com>]

Lay the groundwork for processing #VC exceptions in the handler.
This includes clearing the GHCB, decoding the insn that triggered
this #VC, and continuing execution after the exception has been
processed.

Signed-off-by: Varad Gautam <varad.gautam@suse.com>
---
 lib/x86/amd_sev_vc.c | 78 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/lib/x86/amd_sev_vc.c b/lib/x86/amd_sev_vc.c
index 8226121..142f2cd 100644
--- a/lib/x86/amd_sev_vc.c
+++ b/lib/x86/amd_sev_vc.c
@@ -1,14 +1,92 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
 #include "amd_sev.h"
+#include "svm.h"
 
 extern phys_addr_t ghcb_addr;
 
+static void vc_ghcb_invalidate(struct ghcb *ghcb)
+{
+	ghcb->save.sw_exit_code = 0;
+	memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
+}
+
+static bool vc_decoding_needed(unsigned long exit_code)
+{
+	/* Exceptions don't require to decode the instruction */
+	return !(exit_code >= SVM_EXIT_EXCP_BASE &&
+		 exit_code <= SVM_EXIT_LAST_EXCP);
+}
+
+static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
+{
+	unsigned char buffer[MAX_INSN_SIZE];
+	int ret;
+
+	memcpy(buffer, (unsigned char *)ctxt->regs->rip, MAX_INSN_SIZE);
+
+	ret = insn_decode(&ctxt->insn, buffer, MAX_INSN_SIZE, INSN_MODE_64);
+	if (ret < 0)
+		return ES_DECODE_FAILED;
+	else
+		return ES_OK;
+}
+
+static enum es_result vc_init_em_ctxt(struct es_em_ctxt *ctxt,
+				      struct ex_regs *regs,
+				      unsigned long exit_code)
+{
+	enum es_result ret = ES_OK;
+
+	memset(ctxt, 0, sizeof(*ctxt));
+	ctxt->regs = regs;
+
+	if (vc_decoding_needed(exit_code))
+		ret = vc_decode_insn(ctxt);
+
+	return ret;
+}
+
+static void vc_finish_insn(struct es_em_ctxt *ctxt)
+{
+	ctxt->regs->rip += ctxt->insn.length;
+}
+
+static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
+					 struct ghcb *ghcb,
+					 unsigned long exit_code)
+{
+	enum es_result result;
+
+	switch (exit_code) {
+	default:
+		/*
+		 * Unexpected #VC exception
+		 */
+		result = ES_UNSUPPORTED;
+	}
+
+	return result;
+}
+
 void handle_sev_es_vc(struct ex_regs *regs)
 {
 	struct ghcb *ghcb = (struct ghcb *) ghcb_addr;
+	unsigned long exit_code = regs->error_code;
+	struct es_em_ctxt ctxt;
+	enum es_result result;
+
 	if (!ghcb) {
 		/* TODO: kill guest */
 		return;
 	}
+
+	vc_ghcb_invalidate(ghcb);
+	result = vc_init_em_ctxt(&ctxt, regs, exit_code);
+	if (result == ES_OK)
+		result = vc_handle_exitcode(&ctxt, ghcb, exit_code);
+	if (result == ES_OK)
+		vc_finish_insn(&ctxt);
+
+	return;
 }
-- 
2.32.0