linux-kernel - Re: [PATCH Part2 v5 02/45] iommu/amd: Introduce function to check SEV-SNP support

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Date:   Thu, 16 Sep 2021 19:26:07 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <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 Gonda <pgonda@...gle.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>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part2 v5 02/45] iommu/amd: Introduce function to check
 SEV-SNP support

On Fri, Aug 20, 2021 at 10:58:35AM -0500, Brijesh Singh wrote:
> The SEV-SNP support requires that IOMMU must to enabled, see the IOMMU

s/must to/is/

> 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

"can be used"?

Just say what is going to use it.

> 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 46280e6e1535..bd420fb71126 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3320,3 +3320,33 @@ 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");
> +		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",
> +			       PCI_BUS_NUM(iommu->devid), PCI_SLOT(iommu->devid),
> +			       PCI_FUNC(iommu->devid));
> +			return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sev_snp_supported);

That export is not needed.

> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 32d448050bf7..269abc17b2c3 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -604,6 +604,12 @@ 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 {};
> @@ -999,6 +1005,9 @@ static inline struct iommu_fwspec *dev_iommu_fwspec_get(struct device *dev)
>  {
>  	return NULL;
>  }
> +
> +static inline bool iommu_sev_snp_supported(void) { return false; }
> +

Most of those stubs and ifdeffery is not needed if you put the function
itself in

#ifdef CONFIG_AMD_MEM_ENCRYPT

...

#endif

as it is called by sev.c only, AFAICT, and latter is enabled by
CONFIG_AMD_MEM_ENCRYPT anyway.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette