linux-kernel - Re: [PATCH] x86/sev-es: Do not use copy_from_kernel

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Message-ID: <20230908151333.GL19320@noisy.programming.kicks-ass.net>
Date:   Fri, 8 Sep 2023 17:13:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Adam Dunlap <acdunlap@...gle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nikunj A Dadhania <nikunj@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Joerg Roedel <jroedel@...e.de>, Jacob Xu <jacobhxu@...gle.com>
Subject: Re: [PATCH] x86/sev-es: Do not use copy_from_kernel_nofault in early
 #VC handler

On Fri, Sep 08, 2023 at 07:48:58AM -0700, Dave Hansen wrote:
> On 9/8/23 06:13, Tom Lendacky wrote:
> > On 9/7/23 14:12, Dave Hansen wrote:
> >> But seriously, is it even *possible* to spin up a SEV-SNP VM what
> >> doesn't have NX?
> > 
> > It is a common path, so while an SEV guest would have NX support, you
> > would first have to determine that it is an SEV guest. That would take
> > issuing a CPUID instruction in order to determine if a particular MSR
> > can be read...
> 
> I was thinking more along the lines of telling folks that if they want
> to turn SEV-SNP support on, they also have to give up on running on a
> !NX system.  That would be a _bit_ nicer than just refusing to boot on
> all !NX systems.

I think there were a very limited amount of !NX P4 class x86_64 systems.
I vote in favour of dropping them into the museum bucket, they get to
run an old kernel.

Andrew and me looked at this a few months ago, but I forgot all details
again :/