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Date:   Thu, 21 Jan 2021 17:58:45 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Sean Christopherson <seanjc@google.com>
Cc:     kernel test robot <lkp@intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        kbuild-all@lists.01.org, clang-built-linux@googlegroups.com,
        X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 11/19] x86/sev-es: Convert to insn_decode()
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On Mon, Dec 28, 2020 at 11:15:11AM -0800, Sean Christopherson wrote:
> Alternatively, could the kernel case use insn_decode_regs()?  If
> vc_fetch_insn_kernel() were also modified to mirror insn_fetch_from_user(), the
> two code paths could be unified except for the the fetch and the PFEC.  E.g.

Personal Firearms Eligibility Check?

In any case, I prefer simple, easy to follow code at a quick glance.
Stuff like...

> 
> static int vc_fetch_insn_kernel(struct es_em_ctxt *ctxt,
> 				unsigned char *buffer)
> {
> 	if (copy_from_kernel_nofault(buffer, (unsigned char *)ctxt->regs->ip, MAX_INSN_SIZE))
> 		return 0;
> 
> 	return MAX_INSN_SIZE;
> }
> 
> static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
> {
> 	char buffer[MAX_INSN_SIZE];
> 	int nbytes;
> 
> 	if (user_mode(ctxt->regs))
> 		nbytes = insn_fetch_from_user(ctxt->regs, buffer);
> 	else
> 		nbytes = vc_fetch_insn_kernel(ctxt, buffer);
> 
> 	if (!nbytes) {
> 		ctxt->fi.vector     = X86_TRAP_PF;
> 		ctxt->fi.error_code = X86_PF_INSTR;
> 		if (user_mode(ctxt->regs))

... this second repeated check here is not what I would call that.

But this is my personal preference only so it's up for a vote now.

:-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette