linux-kernel - Re: [PATCH Part2 v6 02/49] iommu/amd: Introduce function to check SEV-SNP support

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Date:   Tue, 21 Jun 2022 11:50:59 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     "Kalra, Ashish" <Ashish.Kalra@....com>
Cc:     "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        "Roth, Michael" <Michael.Roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>, Marc Orr <marcorr@...gle.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Alper Gun <alpergun@...gle.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        "jarkko@...nel.org" <jarkko@...nel.org>
Subject: Re: [PATCH Part2 v6 02/49] iommu/amd: Introduce function to check
 SEV-SNP support

On Tue, Jun 21, 2022 at 11:45 AM Kalra, Ashish <Ashish.Kalra@....com> wrote:
>
> [AMD Official Use Only - General]
>
> Hello Peter,
>
> >> +bool iommu_sev_snp_supported(void)
> >> +{
> >> +       struct amd_iommu *iommu;
> >> +
> >> +       /*
> >> +        * The SEV-SNP support requires that IOMMU must be enabled, and is
> >> +        * not configured in the passthrough mode.
> >> +        */
> >> +       if (no_iommu || iommu_default_passthrough()) {
> >> +               pr_err("SEV-SNP: IOMMU is either disabled or
> >> + configured in passthrough mode.\n");
>
> > Like below could this say something like snp support is disabled because of iommu settings.
>
> Here we may need to be more precise with the error information indicating why SNP is not enabled.
> Please note that this patch may actually become part of the IOMMU + SNP patch series, where
> additional checks are done, for example, not enabling SNP if IOMMU v2 page tables are enabled,
> so precise error information will be useful here.

I agree we should be more precise. I just thought we should explicitly
state something like: "SEV-SNP: IOMMU is either disabled or configured
in passthrough mode, SNP cannot be supported".