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Date:   Wed, 8 Apr 2020 17:09:34 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [PATCH 3/4] x86,module: Detect VMX vs SLD conflicts
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        <20200407111007.352324393@infradead.org>
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On Tue, 07 Apr 2020 13:02:39 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> +static bool insn_is_vmx(struct insn *insn)
> +{
> +	u8 modrm = insn->modrm.bytes[0];
> +	u8 modrm_mod = X86_MODRM_MOD(modrm);
> +	u8 modrm_reg = X86_MODRM_REG(modrm);
> +
> +	u8 prefix = insn->prefixes.bytes[0];

This should be the last prefix,

	u8 prefix = insn->prefixes.bytes[3];

(The last prefix always copied on the bytes[3])

> +
> +	if (insn->opcode.bytes[0] != 0x0f)
> +		return false;
> +
> +	switch (insn->opcode.bytes[1]) {
> +	case 0x01:
> +		switch (insn->opcode.bytes[2]) {

Sorry, VMCALL etc. is in Grp7 (0f 01), the 3rd code is embedded
in modrm instead of opcode. Thus it should be,

		switch (insn->modrm.value) {

> +		case 0xc1: /* VMCALL */
> +		case 0xc2: /* VMLAUNCH */
> +		case 0xc3: /* VMRESUME */
> +		case 0xc4: /* VMXOFF */

		case 0xd4:	/* VMFUNC */

> +			return true;
> +
> +		default:
> +			break;
> +		}
> +		break;
> +
> +	case 0x78: /* VMREAD */
> +	case 0x79: /* VMWRITE */

		return !insn_is_evex(insn);

With EVEX prefix, these becomes vcvt* instructions.

> +	case 0xc7:
> +		/* VMPTRLD, VMPTRST, VMCLEAR, VMXON */
> +		if (modrm_mod == 0x03)
> +			break;
> +
> +		if ((modrm_reg == 6 && (!prefix || prefix == 0x66 || prefix == 0xf3)) ||
> +		    (modrm_reg == 7 && (!prefix || prefix == 0xf3)))
> +			return true;
> +
> +		break;
> +
> +	default:
> +		break;
> +	}
> +
> +	return false;
> +}


Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>