[PATCH Part1 RFC v4 22/36] x86/sev: move MSR-based VMGEXITs for CPUID to helper

[Brijesh Singh <brijesh.singh@xxxxxxx>]

From: Michael Roth <michael.roth@xxxxxxx>

This code will also be used later for SEV-SNP-validated CPUID code in
some cases, so move it to a common helper.

Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/kernel/sev-shared.c | 84 +++++++++++++++++++++++++-----------
 1 file changed, 58 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index be4025f14b4f..4884de256a49 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -184,6 +184,58 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
 	return ret;
 }
 
+static int sev_es_cpuid_msr_proto(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
+				  u32 *ecx, u32 *edx)
+{
+	u64 val;
+
+	if (eax) {
+		sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(func, GHCB_CPUID_REQ_EAX));
+		VMGEXIT();
+		val = sev_es_rd_ghcb_msr();
+
+		if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+			return -EIO;
+
+		*eax = (val >> 32);
+	}
+
+	if (ebx) {
+		sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(func, GHCB_CPUID_REQ_EBX));
+		VMGEXIT();
+		val = sev_es_rd_ghcb_msr();
+
+		if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+			return -EIO;
+
+		*ebx = (val >> 32);
+	}
+
+	if (ecx) {
+		sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(func, GHCB_CPUID_REQ_ECX));
+		VMGEXIT();
+		val = sev_es_rd_ghcb_msr();
+
+		if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+			return -EIO;
+
+		*ecx = (val >> 32);
+	}
+
+	if (edx) {
+		sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(func, GHCB_CPUID_REQ_EDX));
+		VMGEXIT();
+		val = sev_es_rd_ghcb_msr();
+
+		if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+			return -EIO;
+
+		*edx = (val >> 32);
+	}
+
+	return 0;
+}
+
 /*
  * Boot VC Handler - This is the first VC handler during boot, there is no GHCB
  * page yet, so it only supports the MSR based communication with the
@@ -192,39 +244,19 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
 void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
 {
 	unsigned int fn = lower_bits(regs->ax, 32);
-	unsigned long val;
+	u32 eax, ebx, ecx, edx;
 
 	/* Only CPUID is supported via MSR protocol */
 	if (exit_code != SVM_EXIT_CPUID)
 		goto fail;
 
-	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EAX));
-	VMGEXIT();
-	val = sev_es_rd_ghcb_msr();
-	if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+	if (sev_es_cpuid_msr_proto(fn, 0, &eax, &ebx, &ecx, &edx))
 		goto fail;
-	regs->ax = val >> 32;
 
-	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EBX));
-	VMGEXIT();
-	val = sev_es_rd_ghcb_msr();
-	if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
-		goto fail;
-	regs->bx = val >> 32;
-
-	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_ECX));
-	VMGEXIT();
-	val = sev_es_rd_ghcb_msr();
-	if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
-		goto fail;
-	regs->cx = val >> 32;
-
-	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EDX));
-	VMGEXIT();
-	val = sev_es_rd_ghcb_msr();
-	if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
-		goto fail;
-	regs->dx = val >> 32;
+	regs->ax = eax;
+	regs->bx = ebx;
+	regs->cx = ecx;
+	regs->dx = edx;
 
 	/*
 	 * This is a VC handler and the #VC is only raised when SEV-ES is
-- 
2.17.1