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From:   Andy Lutomirski <luto@kernel.org>
Date:   Wed, 12 Feb 2020 13:42:48 -0800
Message-ID: <CALCETrVRmg88xY0s4a2CONXQ3fgvCKXpW2eYJRJGhqQLneoGqQ@mail.gmail.com>
Subject: Re: [PATCH 38/62] x86/sev-es: Handle instruction fetches from user-space
To:     Joerg Roedel <joro@8bytes.org>
Cc:     X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Juergen Gross <jgross@suse.com>,
        Kees Cook <keescook@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>
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On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@8bytes.org> wrote:
>
> From: Joerg Roedel <jroedel@suse.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