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Date:   Thu, 11 Jun 2020 12:05:19 +0200
From:   Joerg Roedel <joro@8bytes.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     x86@kernel.org, hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
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        Juergen Gross <jgross@suse.com>,
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        Cfir Cohen <cfir@google.com>,
        Erdem Aktas <erdemaktas@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mike Stunes <mstunes@vmware.com>,
        Joerg Roedel <jroedel@suse.de>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v3 40/75] x86/sev-es: Compile early handler code into
 kernel image
Message-ID: <20200611100519.GB32093@8bytes.org>
References: <20200428151725.31091-1-joro@8bytes.org>
 <20200428151725.31091-41-joro@8bytes.org>
 <20200520091415.GC1457@zn.tnic>
 <20200604115413.GB30945@8bytes.org>
 <20200604151945.GB2246@zn.tnic>
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On Thu, Jun 04, 2020 at 05:19:53PM +0200, Borislav Petkov wrote:
> On Thu, Jun 04, 2020 at 01:54:13PM +0200, Joerg Roedel wrote:
> > It is not only the trace-point, this would also eliminate exception
> > handling in case the MSR access triggers a #GP. The "Unhandled MSR
> > read/write" messages would turn into a "General Protection Fault"
> > message.
> 
> But the early ones can trigger a #GP too. And there we can't handle
> those #GPs.
> 
> Why would the late ones need exception handling all of a sudden? And
> for the GHCB MSR, of all MSRs which the SEV-ES guest has used so far to
> bootstrap?!

For example when there is a bug in the code which triggers an SEV-ES-only
code-path at runtime on bare-metal or in a non-SEV-ES VM. When the MSR
is accessed accidentially in that code-path the exception handling will
be helpful.


	Joerg