Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

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On 11/7/2023 4:08 PM, Borislav Petkov wrote:
  static int __init snp_rmptable_init(void)
  {
-	int family, model;
-
-	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+	if (!amd_iommu_snp_en)
  		return 0;


We will still need some method to tell the IOMMU driver if SNP support/feature is disabled by this function, for example, when CPU family and model is not supported by SNP and we jump to no_snp label.

The reliable way for this to work is to ensure snp_rmptable_init() is called before IOMMU initialization and then IOMMU initialization depends on SNP feature flag setup by snp_rmptable_init() to enable SNP support on IOMMU or not.

If snp_rmptable_init() is called after IOMMU initialization and it detects an issue with SNP support it will clear the SNP feature but the IOMMU driver does not get notified about it, therefore, snp_rmptable_init() should get called before IOMMU initialization or as part of IOMMU initialization, for example, amd_iommu_enable() calling snp_rmptable_init() before calling iommu_snp_enable().

Thanks,
Ashish





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