linux-kernel - Re: [PATCH 7/8] tools/objtool: Check for use of the ENQCMD instruction in the kernel

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Date:   Wed, 22 Sep 2021 23:03:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Jacob Jun Pan <jacob.jun.pan@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/8] tools/objtool: Check for use of the ENQCMD
 instruction in the kernel

On Mon, Sep 20, 2021 at 07:23:48PM +0000, Fenghua Yu wrote:


> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e5947fbb9e7a..91d13521d9d6 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -3133,6 +3133,21 @@ static int validate_reachable_instructions(struct objtool_file *file)
>  	return 0;
>  }
>  
> +static int validate_enqcmd(struct objtool_file *file)
> +{
> +	struct instruction *insn;
> +
> +	for_each_insn(file, insn) {
> +		if (insn->type == INSN_ENQCMD) {
> +			WARN_FUNC("enqcmd instruction", insn->sec,
> +				  insn->offset);
> +			return 1;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  int check(struct objtool_file *file)
>  {
>  	int ret, warnings = 0;
> @@ -3147,6 +3162,11 @@ int check(struct objtool_file *file)
>  	if (list_empty(&file->insn_list))
>  		goto out;
>  
> +	ret = validate_enqcmd(file);
> +	if (ret < 0)
> +		goto out;
> +	warnings += ret;
> +
>  	if (vmlinux && !validate_dup) {
>  		ret = validate_vmlinux_functions(file);
>  		if (ret < 0)

Since you're making it a fatal error, before doing much of anything
else, you might at well fail decode and keep it all in the x86/decode.c
file, no need to spread this 'knowledge' any further.

There's no actual state associated with it, you just want to avoid the
instruction being present.

Much simpler patch too.