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

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Message-ID: <CAMkAt6r+WSYXLZj-Bs5jpo4CR3+H5cpND0GHjsmgPacBK1GH_Q@mail.gmail.com>
Date:   Tue, 21 Jun 2022 09:28:04 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Ashish Kalra <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-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>,
        Michael Roth <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
Subject: Re: [PATCH Part2 v6 02/49] iommu/amd: Introduce function to check
 SEV-SNP support

On Mon, Jun 20, 2022 at 4:59 PM Ashish Kalra <Ashish.Kalra@....com> wrote:
>
> From: Brijesh Singh <brijesh.singh@....com>
>
> The SEV-SNP support requires that IOMMU must to enabled, see the IOMMU
> spec section 2.12 for further details. If IOMMU is not enabled or the
> SNPSup extended feature register is not set then the SNP_INIT command
> (used for initializing firmware) will fail.
>
> The iommu_sev_snp_supported() can be used to check if IOMMU supports the
> SEV-SNP feature.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  drivers/iommu/amd/init.c | 30 ++++++++++++++++++++++++++++++
>  include/linux/iommu.h    |  9 +++++++++
>  2 files changed, 39 insertions(+)
>
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 1a3ad58ba846..82be8067ddf5 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3361,3 +3361,33 @@ int amd_iommu_pc_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn, u64
>
>         return iommu_pc_get_set_reg(iommu, bank, cntr, fxn, value, true);
>  }
> +
> +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.

> +               return false;
> +       }
> +
> +       /*
> +        * Iterate through all the IOMMUs and verify the SNPSup feature is
> +        * enabled.
> +        */
> +       for_each_iommu(iommu) {
> +               if (!iommu_feature(iommu, FEATURE_SNP)) {
> +                       pr_err("SNPSup is disabled (devid: %02x:%02x.%x)\n",

SNPSup might not be obvious to readers, what about " SNP Support is
disabled ...".

Also should this have the "SEV-SNP:" prefix like the above log?

> +                              PCI_BUS_NUM(iommu->devid), PCI_SLOT(iommu->devid),
> +                              PCI_FUNC(iommu->devid));
> +                       return false;
> +               }
> +       }
> +
> +       return true;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sev_snp_supported);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 9208eca4b0d1..fecb72e1b11b 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -675,6 +675,12 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev,
>  void iommu_sva_unbind_device(struct iommu_sva *handle);
>  u32 iommu_sva_get_pasid(struct iommu_sva *handle);
>
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +bool iommu_sev_snp_supported(void);
> +#else
> +static inline bool iommu_sev_snp_supported(void) { return false; }
> +#endif
> +
>  #else /* CONFIG_IOMMU_API */
>
>  struct iommu_ops {};
> @@ -1031,6 +1037,9 @@ static inline struct iommu_fwspec *dev_iommu_fwspec_get(struct device *dev)
>  {
>         return NULL;
>  }
> +
> +static inline bool iommu_sev_snp_supported(void) { return false; }
> +
>  #endif /* CONFIG_IOMMU_API */
>
>  /**
> --
> 2.25.1
>