x86/sev: Cleanup vc_handle_msr()

Carve out the MSR_SVSM_CAA into a helper with the suggestion that
upcoming future users should do the same. Rename that silly exit_info_1
into what it actually means in this function - whether the MSR access is
a read or a write.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Reviewed-by: Pankaj Gupta <[email protected]>
Link: https://lore.kernel.org/r/20241106172647.GAZyum1zngPDwyD2IJ@fat_crate.local

Author: bp3tk0v

arch/x86/coco/sev/core.c

@@ -1406,35 +1406,39 @@ int __init sev_es_efi_map_ghcbs(pgd_t *pgd)
 	return 0;
 }
 
+/* Writes to the SVSM CAA MSR are ignored */
+static enum es_result __vc_handle_msr_caa(struct pt_regs *regs, bool write)
+{
+	if (write)
+		return ES_OK;
+
+	regs->ax = lower_32_bits(this_cpu_read(svsm_caa_pa));
+	regs->dx = upper_32_bits(this_cpu_read(svsm_caa_pa));
+
+	return ES_OK;
+}
+
 static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 {
 	struct pt_regs *regs = ctxt->regs;
 	enum es_result ret;
-	u64 exit_info_1;
+	bool write;
 
 	/* Is it a WRMSR? */
-	exit_info_1 = (ctxt->insn.opcode.bytes[1] == 0x30) ? 1 : 0;
-
-	if (regs->cx == MSR_SVSM_CAA) {
-		/* Writes to the SVSM CAA msr are ignored */
-		if (exit_info_1)
-			return ES_OK;
-
-		regs->ax = lower_32_bits(this_cpu_read(svsm_caa_pa));
-		regs->dx = upper_32_bits(this_cpu_read(svsm_caa_pa));
+	write = ctxt->insn.opcode.bytes[1] == 0x30;
 
-		return ES_OK;
-	}
+	if (regs->cx == MSR_SVSM_CAA)
+		return __vc_handle_msr_caa(regs, write);
 
 	ghcb_set_rcx(ghcb, regs->cx);
-	if (exit_info_1) {
+	if (write) {
 		ghcb_set_rax(ghcb, regs->ax);
 		ghcb_set_rdx(ghcb, regs->dx);
 	}
 
-	ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_MSR, exit_info_1, 0);
+	ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_MSR, write, 0);
 
-	if ((ret == ES_OK) && (!exit_info_1)) {
+	if ((ret == ES_OK) && !write) {
 		regs->ax = ghcb->save.rax;
 		regs->dx = ghcb->save.rdx;
 	}