linux-kernel - Re: [PATCH v2 2/2] x86/sev-es: Only set x86_virt

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Date:   Mon, 2 Oct 2023 14:46:25 -0700
From:   Adam Dunlap <acdunlap@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        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>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Kim Phillips <kim.phillips@....com>,
        Juergen Gross <jgross@...e.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....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>,
        Peter Gonda <pgonda@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Khalid ElMously <khalid.elmously@...onical.com>,
        Jacob Xu <jacobhxu@...gle.com>, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 2/2] x86/sev-es: Only set x86_virt_bits to correct value

On Mon, Oct 2, 2023 at 2:41 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 10/2/23 13:04, Nathan Chancellor wrote:
> > On Mon, Sep 11, 2023 at 05:27:03PM -0700, Adam Dunlap wrote:
> >> Instead of setting x86_virt_bits to a possibly-correct value and then
> >> correcting it later, do all the necessary checks before setting it.
> >>
> >> At this point, the #VC handler references boot_cpu_data.x86_virt_bits,
> >> and in the previous version, it would be triggered by the cpuids between
> >> the point at which it is set to 48 and when it is set to the correct
> >> value.
> >>
> >> Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
> >> Signed-off-by: Adam Dunlap <acdunlap@...gle.com>
> > Our continuous integration started seeing panics when booting ARCH=i386
> > without KVM after this change landed in -tip as commit fbf6449f84bf
> > ("x86/sev-es: Set x86_virt_bits to the correct value straight away,
> > instead of a two-phase approach"):
>
> I can't reproduce this, but I'm running a gcc-built kernel and I haven't
> tried very hard to replicate your qemu setup.
>
> I did notice, though, that the patch in question forgot to move one
> assignment.  Could you see if the attached patch fixes things for you?

I reproduced the issue as Nathan described and your attached patch fixes it
for me.