linux-kernel - Re: [PATCH v3 1/7] iommu/amd: Warn when found inconsistency EFR mask

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Message-ID: <YrQizrI5lR3ki37B@8bytes.org>
Date:   Thu, 23 Jun 2022 10:22:38 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        robin.murphy@....com, ashish.kalra@....com, vasant.hegde@....com,
        thomas.lendacky@....com
Subject: Re: [PATCH v3 1/7] iommu/amd: Warn when found inconsistency EFR mask

On Wed, Jun 22, 2022 at 12:11:25PM -0500, Suravee Suthikulpanit wrote:
>  #ifdef CONFIG_IRQ_REMAP
> +/*
> + * Iterate through all the IOMMUs to verify if the specified
> + * EFR bitmask of IOMMU feature are set.
> + * Warn and return false if found inconsistency.
> + */
>  static bool check_feature_on_all_iommus(u64 mask)
>  {
>  	bool ret = false;
>  	struct amd_iommu *iommu;
>  
>  	for_each_iommu(iommu) {
> -		ret = iommu_feature(iommu, mask);
> -		if (!ret)
> +		bool tmp = iommu_feature(iommu, mask);
> +
> +		if ((ret != tmp) &&
> +		    !list_is_first(&iommu->list, &amd_iommu_list)) {
> +			pr_err(FW_BUG "Found inconsistent EFR mask (%#llx) on iommu%d (%04x:%02x:%02x.%01x).\n",
> +			       mask, iommu->index, iommu->pci_seg->id, PCI_BUS_NUM(iommu->devid),
> +			       PCI_SLOT(iommu->devid), PCI_FUNC(iommu->devid));
>  			return false;
> +		}
> +		ret = tmp;

It is better to implement this by introducing a global feature mask,
which represents the minial set of features supported by any IOMMU in
the system.

The warning is then something like:

	if ((global_feature_mask & iommu_features) != global_feature_mask)
		pr_warn(...);

This also makes the global variable to track SNP support obsolete.

Regards,

	Joerg