[RFC v2-fix-v2 1/2] x86/sev-es: Abstract out MMIO instruction decoding

[Kuppuswamy Sathyanarayanan]

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

For regular virtual machine, MMIO is handled by the VMM: KVM
emulates instruction that caused MMIO. But, this model doesn't
work for a secure VMs (like SEV or TDX) as VMM doesn't have
access to the guest memory and register state. VMM needs
assistance in handling MMIO: it induces exception in the guest.
Guest has to decode the instruction and handle it on its own.

Instruction decoding logic is similar between AMD SEV and TDX
code. So extract the decoding code to insn-eval.c where it can
be used by both SEV and TDX.

This code adds no functional changes. It is only build-tested
for SEV.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
---
 arch/x86/include/asm/insn-eval.h |  13 +++
 arch/x86/kernel/sev.c            | 171 ++++++++-----------------------
 arch/x86/lib/insn-eval.c         | 102 ++++++++++++++++++
 3 files changed, 155 insertions(+), 131 deletions(-)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 91d7182ad2d6..4a4ca7e7be66 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -19,6 +19,7 @@ bool insn_has_rep_prefix(struct insn *insn);
 void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
 int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs);
 int insn_get_modrm_reg_off(struct insn *insn, struct pt_regs *regs);
+void *insn_get_modrm_reg_ptr(struct insn *insn, struct pt_regs *regs);
 unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx);
 int insn_get_code_seg_params(struct pt_regs *regs);
 int insn_fetch_from_user(struct pt_regs *regs,
@@ -28,4 +29,16 @@ int insn_fetch_from_user_inatomic(struct pt_regs *regs,
 bool insn_decode_from_regs(struct insn *insn, struct pt_regs *regs,
 			   unsigned char buf[MAX_INSN_SIZE], int buf_size);
 
+enum mmio_type {
+	MMIO_DECODE_FAILED,
+	MMIO_WRITE,
+	MMIO_WRITE_IMM,
+	MMIO_READ,
+	MMIO_READ_ZERO_EXTEND,
+	MMIO_READ_SIGN_EXTEND,
+	MMIO_MOVS,
+};
+
+enum mmio_type insn_decode_mmio(struct insn *insn, int *bytes);
+
 #endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 651b81cd648e..f7a743d122eb 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -789,22 +789,6 @@ static void __init vc_early_forward_exception(struct es_em_ctxt *ctxt)
 	do_early_exception(ctxt->regs, trapnr);
 }
 
-static long *vc_insn_get_reg(struct es_em_ctxt *ctxt)
-{
-	long *reg_array;
-	int offset;
-
-	reg_array = (long *)ctxt->regs;
-	offset    = insn_get_modrm_reg_off(&ctxt->insn, ctxt->regs);
-
-	if (offset < 0)
-		return NULL;
-
-	offset /= sizeof(long);
-
-	return reg_array + offset;
-}
-
 static long *vc_insn_get_rm(struct es_em_ctxt *ctxt)
 {
 	long *reg_array;
@@ -852,76 +836,6 @@ static enum es_result vc_do_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
 	return sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, exit_info_1, exit_info_2);
 }
 
-static enum es_result vc_handle_mmio_twobyte_ops(struct ghcb *ghcb,
-						 struct es_em_ctxt *ctxt)
-{
-	struct insn *insn = &ctxt->insn;
-	unsigned int bytes = 0;
-	enum es_result ret;
-	int sign_byte;
-	long *reg_data;
-
-	switch (insn->opcode.bytes[1]) {
-		/* MMIO Read w/ zero-extension */
-	case 0xb6:
-		bytes = 1;
-		fallthrough;
-	case 0xb7:
-		if (!bytes)
-			bytes = 2;
-
-		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
-		if (ret)
-			break;
-
-		/* Zero extend based on operand size */
-		reg_data = vc_insn_get_reg(ctxt);
-		if (!reg_data)
-			return ES_DECODE_FAILED;
-
-		memset(reg_data, 0, insn->opnd_bytes);
-
-		memcpy(reg_data, ghcb->shared_buffer, bytes);
-		break;
-
-		/* MMIO Read w/ sign-extension */
-	case 0xbe:
-		bytes = 1;
-		fallthrough;
-	case 0xbf:
-		if (!bytes)
-			bytes = 2;
-
-		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
-		if (ret)
-			break;
-
-		/* Sign extend based on operand size */
-		reg_data = vc_insn_get_reg(ctxt);
-		if (!reg_data)
-			return ES_DECODE_FAILED;
-
-		if (bytes == 1) {
-			u8 *val = (u8 *)ghcb->shared_buffer;
-
-			sign_byte = (*val & 0x80) ? 0xff : 0x00;
-		} else {
-			u16 *val = (u16 *)ghcb->shared_buffer;
-
-			sign_byte = (*val & 0x8000) ? 0xff : 0x00;
-		}
-		memset(reg_data, sign_byte, insn->opnd_bytes);
-
-		memcpy(reg_data, ghcb->shared_buffer, bytes);
-		break;
-
-	default:
-		ret = ES_UNSUPPORTED;
-	}
-
-	return ret;
-}
-
 /*
  * The MOVS instruction has two memory operands, which raises the
  * problem that it is not known whether the access to the source or the
@@ -989,83 +903,78 @@ static enum es_result vc_handle_mmio_movs(struct es_em_ctxt *ctxt,
 		return ES_RETRY;
 }
 
-static enum es_result vc_handle_mmio(struct ghcb *ghcb,
-				     struct es_em_ctxt *ctxt)
+static enum es_result vc_handle_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 {
 	struct insn *insn = &ctxt->insn;
 	unsigned int bytes = 0;
+	enum mmio_type mmio;
 	enum es_result ret;
+	u8 sign_byte;
 	long *reg_data;
 
-	switch (insn->opcode.bytes[0]) {
-	/* MMIO Write */
-	case 0x88:
-		bytes = 1;
-		fallthrough;
-	case 0x89:
-		if (!bytes)
-			bytes = insn->opnd_bytes;
+	mmio = insn_decode_mmio(insn, &bytes);
+	if (mmio == MMIO_DECODE_FAILED)
+		return ES_DECODE_FAILED;
 
-		reg_data = vc_insn_get_reg(ctxt);
+	if (mmio != MMIO_WRITE_IMM && mmio != MMIO_MOVS) {
+		reg_data = insn_get_modrm_reg_ptr(insn, ctxt->regs);
 		if (!reg_data)
 			return ES_DECODE_FAILED;
+	}
 
+	switch (mmio) {
+	case MMIO_WRITE:
 		memcpy(ghcb->shared_buffer, reg_data, bytes);
-
 		ret = vc_do_mmio(ghcb, ctxt, bytes, false);
 		break;
-
-	case 0xc6:
-		bytes = 1;
-		fallthrough;
-	case 0xc7:
-		if (!bytes)
-			bytes = insn->opnd_bytes;
-
+	case MMIO_WRITE_IMM:
 		memcpy(ghcb->shared_buffer, insn->immediate1.bytes, bytes);
-
 		ret = vc_do_mmio(ghcb, ctxt, bytes, false);
 		break;
-
-		/* MMIO Read */
-	case 0x8a:
-		bytes = 1;
-		fallthrough;
-	case 0x8b:
-		if (!bytes)
-			bytes = insn->opnd_bytes;
-
+	case MMIO_READ:
 		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
 		if (ret)
 			break;
 
-		reg_data = vc_insn_get_reg(ctxt);
-		if (!reg_data)
-			return ES_DECODE_FAILED;
-
 		/* Zero-extend for 32-bit operation */
 		if (bytes == 4)
 			*reg_data = 0;
 
 		memcpy(reg_data, ghcb->shared_buffer, bytes);
 		break;
+	case MMIO_READ_ZERO_EXTEND:
+		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
+		if (ret)
+			break;
+
+		memset(reg_data, 0, insn->opnd_bytes);
+		memcpy(reg_data, ghcb->shared_buffer, bytes);
+		break;
+	case MMIO_READ_SIGN_EXTEND:
+		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
+		if (ret)
+			break;
 
-		/* MOVS instruction */
-	case 0xa4:
-		bytes = 1;
-		fallthrough;
-	case 0xa5:
-		if (!bytes)
-			bytes = insn->opnd_bytes;
+		if (bytes == 1) {
+			u8 *val = (u8 *)ghcb->shared_buffer;
 
-		ret = vc_handle_mmio_movs(ctxt, bytes);
+			sign_byte = (*val & 0x80) ? 0xff : 0x00;
+		} else {
+			u16 *val = (u16 *)ghcb->shared_buffer;
+
+			sign_byte = (*val & 0x8000) ? 0xff : 0x00;
+		}
+
+		/* Sign extend based on operand size */
+		memset(reg_data, sign_byte, insn->opnd_bytes);
+		memcpy(reg_data, ghcb->shared_buffer, bytes);
 		break;
-		/* Two-Byte Opcodes */
-	case 0x0f:
-		ret = vc_handle_mmio_twobyte_ops(ghcb, ctxt);
+	case MMIO_MOVS:
+		ret = vc_handle_mmio_movs(ctxt, bytes);
 		break;
 	default:
 		ret = ES_UNSUPPORTED;
+		break;
 	}
 
 	return ret;
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index a67afd74232c..81e8fe0bdc39 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -850,6 +850,26 @@ int insn_get_modrm_reg_off(struct insn *insn, struct pt_regs *regs)
 	return get_reg_offset(insn, regs, REG_TYPE_REG);
 }
 
+/**
+ * insn_get_modrm_reg_ptr() - Obtain register pointer based on ModRM byte
+ * @insn:	Instruction containing the ModRM byte
+ * @regs:	Register values as seen when entering kernel mode
+ *
+ * Returns:
+ *
+ * The register indicated by the reg part of the ModRM byte.
+ * The register is obtained as an pointer within pt_regs.
+ */
+void *insn_get_modrm_reg_ptr(struct insn *insn, struct pt_regs *regs)
+{
+	int offset;
+
+	offset = insn_get_modrm_reg_off(insn, regs);
+	if (offset < 0)
+		return NULL;
+	return (void *)regs + offset;
+}
+
 /**
  * get_seg_base_limit() - obtain base address and limit of a segment
  * @insn:	Instruction. Must be valid.
@@ -1539,3 +1559,85 @@ bool insn_decode_from_regs(struct insn *insn, struct pt_regs *regs,
 
 	return true;
 }
+
+/**
+ * insn_decode() - Decode a MMIO instruction
+ * @insn:	Structure to store decoded instruction
+ * @bytes:	Returns size of memory operand
+ *
+ * Decodes instruction that used for Memory-mapped I/O.
+ *
+ * Returns:
+ *
+ * Type of the instruction. Size of memory operand is stored in @bytes.
+ * If decode failed, MMIO_DECODE_FAILED returned.
+ */
+enum mmio_type insn_decode_mmio(struct insn *insn, int *bytes)
+{
+	int type = MMIO_DECODE_FAILED;
+
+	*bytes = 0;
+
+	insn_get_opcode(insn);
+	switch (insn->opcode.bytes[0]) {
+	case 0x88: /* MOV m8,r8 */
+		*bytes = 1;
+		fallthrough;
+	case 0x89: /* MOV m16/m32/m64, r16/m32/m64 */
+		if (!*bytes)
+			*bytes = insn->opnd_bytes;
+		type = MMIO_WRITE;
+		break;
+
+	case 0xc6: /* MOV m8, imm8 */
+		*bytes = 1;
+		fallthrough;
+	case 0xc7: /* MOV m16/m32/m64, imm16/imm32/imm64 */
+		if (!*bytes)
+			*bytes = insn->opnd_bytes;
+		type = MMIO_WRITE_IMM;
+		break;
+
+	case 0x8a: /* MOV r8, m8 */
+		*bytes = 1;
+		fallthrough;
+	case 0x8b: /* MOV r16/r32/r64, m16/m32/m64 */
+		if (!*bytes)
+			*bytes = insn->opnd_bytes;
+		type = MMIO_READ;
+		break;
+
+	case 0xa4: /* MOVS m8, m8 */
+		*bytes = 1;
+		fallthrough;
+	case 0xa5: /* MOVS m16/m32/m64, m16/m32/m64 */
+		if (!*bytes)
+			*bytes = insn->opnd_bytes;
+		type = MMIO_MOVS;
+		break;
+
+	case 0x0f: /* Two-byte instruction */
+		switch (insn->opcode.bytes[1]) {
+		case 0xb6: /* MOVZX r16/r32/r64, m8 */
+			*bytes = 1;
+			fallthrough;
+		case 0xb7: /* MOVZX r32/r64, m16 */
+			if (!*bytes)
+				*bytes = 2;
+			type = MMIO_READ_ZERO_EXTEND;
+			break;
+
+		case 0xbe: /* MOVSX r16/r32/r64, m8 */
+			*bytes = 1;
+			fallthrough;
+		case 0xbf: /* MOVSX r32/r64, m16 */
+			if (!*bytes)
+				*bytes = 2;
+			type = MMIO_READ_SIGN_EXTEND;
+			break;
+		}
+		break;
+	}
+
+	return type;
+}
-- 
2.25.1