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

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Message-ID: <SN6PR12MB27673AC95A577D5468A949598E819@SN6PR12MB2767.namprd12.prod.outlook.com>
Date:   Tue, 5 Jul 2022 13:56:00 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
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Subject: RE: [PATCH Part2 v6 02/49] iommu/amd: Introduce function to check
 SEV-SNP support

[AMD Official Use Only - General]

Hello Boris,

>> +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);

> Why is this function exported?

This function is required to ensure that IOMMU supports the SEV-SNP feature before enabling the SNP feature
and calling SNP_INIT. This IOMMU support check is done in the AMD IOMMU driver with the 
iommu_sev_snp_supported() function so it is exported by the IOMMU driver and called by sev module
later for SNP initialization in snp_rmptable_init(). 

Thanks,
Ashish