linux-kernel - [tip: x86/misc] x86/insn-eval: Introduce insn_decode

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Date:   Tue, 30 Nov 2021 22:56:35 -0000
From:   "tip-bot2 for Kirill A. Shutemov" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/misc] x86/insn-eval: Introduce insn_decode_mmio()

The following commit has been merged into the x86/misc branch of tip:

Commit-ID:     70a81f99e45b15b3e77f70720742545e1c7541da
Gitweb:        https://git.kernel.org/tip/70a81f99e45b15b3e77f70720742545e1c7541da
Author:        Kirill A. Shutemov <kirill@...temov.name>
AuthorDate:    Tue, 30 Nov 2021 21:49:32 +03:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Tue, 30 Nov 2021 14:53:19 -08:00

x86/insn-eval: Introduce insn_decode_mmio()

In preparation for sharing MMIO instruction decode between SEV-ES and
TDX, factor out the common decode into a new insn_decode_mmio() helper.

For regular virtual machine, MMIO is handled by the VMM and KVM
emulates instructions 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. So, for TDX or SEV VMM needs
assistance in handling MMIO. It induces exception in the guest. Guest
has to decode the instruction and handle it on its own.

The code is based on the current SEV MMIO implementation.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Tested-by: Joerg Roedel <jroedel@...e.de>
Acked-by: Tom Lendacky <thomas.lendacky@....com>
Link: https://lkml.kernel.org/r/20211130184933.31005-4-kirill.shutemov@linux.intel.com
---
 arch/x86/include/asm/insn-eval.h | 12 ++++-
 arch/x86/lib/insn-eval.c         | 84 +++++++++++++++++++++++++++++++-
 2 files changed, 96 insertions(+)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 33ae404..43785ee 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -30,4 +30,16 @@ 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/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 8df6236..53e57ef 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1560,3 +1560,87 @@ bool insn_decode_from_regs(struct insn *insn, struct pt_regs *regs,
 
 	return true;
 }
+
+/**
+ * insn_decode_mmio() - 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 the memory operand is stored in
+ * @bytes. If decode failed, MMIO_DECODE_FAILED returned.
+ */
+enum mmio_type insn_decode_mmio(struct insn *insn, int *bytes)
+{
+	enum mmio_type type = MMIO_DECODE_FAILED;
+
+	*bytes = 0;
+
+	if (insn_get_opcode(insn))
+		return MMIO_DECODE_FAILED;
+
+	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;
+}