linux-kernel - [PATCHv4 2/4] x86/insn-eval: Introduce insn_get_modrm_reg

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Message-Id: <20211130184933.31005-3-kirill.shutemov@linux.intel.com>
Date:   Tue, 30 Nov 2021 21:49:31 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Joerg Roedel <jroedel@...e.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Nakajima, Jun" <jun.nakajima@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCHv4 2/4] x86/insn-eval: Introduce insn_get_modrm_reg_ptr()

From: "Kirill A. Shutemov" <kirill@...temov.name>

The helper returns a pointer to the register indicated by
ModRM byte.

It's going to replace vc_insn_get_reg() in the SEV MMIO
implementation. TDX MMIO implementation will also use it.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...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>
---
 arch/x86/include/asm/insn-eval.h |  1 +
 arch/x86/lib/insn-eval.c         | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 4ec3613551e3..33ae4040c7ee 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);
+unsigned long *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_get_effective_ip(struct pt_regs *regs, unsigned long *ip);
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 868d80ea85d9..0168378ee2d4 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -848,6 +848,26 @@ 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 a pointer within pt_regs.
+ */
+unsigned long *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.
-- 
2.32.0