linux-kernel - Re: [PATCH 38/62] x86/sev-es: Handle instruction fetches from user-space

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Date:   Wed, 12 Feb 2020 13:42:48 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 38/62] x86/sev-es: Handle instruction fetches from user-space

On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@...tes.org> wrote:
>
> From: Joerg Roedel <jroedel@...e.de>
>
> When a #VC exception is triggered by user-space the instruction
> decoder needs to read the instruction bytes from user addresses.
> Enhance es_fetch_insn_byte() to safely fetch kernel and user
> instruction bytes.

I realize that this is a somewhat arbitrary point in the series to
complain about this, but: the kernel already has infrastructure to
decode and fix up an instruction-based exception.  See
fixup_umip_exception().  Please refactor code so that you can share
the same infrastructure rather than creating an entirely new thing.

FWIW, the fixup_umip_exception() code seems to have much more robust
segment handling than yours :)

--Andy