linux-kernel - Re: [PATCH 2/2] thunderbolt: Use pre-boot DMA protection on AMD systems

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Message-ID: <YjDDUUeZ/dvUZoDN@infradead.org>
Date:   Tue, 15 Mar 2022 09:48:17 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Will Deacon <will@...nel.org>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        "open list:AMD IOMMU (AMD-VI)" <iommu@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:THUNDERBOLT DRIVER" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 2/2] thunderbolt: Use pre-boot DMA protection on AMD
 systems

On Tue, Mar 15, 2022 at 11:24:55AM -0500, Mario Limonciello wrote:
> -	 * handled natively using IOMMU. It is enabled when IOMMU is
> -	 * enabled and ACPI DMAR table has DMAR_PLATFORM_OPT_IN set.
> +	 * handled natively using IOMMU. It is enabled when the IOMMU is
> +	 * enabled and either:
> +	 * ACPI DMAR table has DMAR_PLATFORM_OPT_IN set
> +	 * or
> +	 * ACPI IVRS table has DMA_REMAP bitset
>  	 */
>  	return sprintf(buf, "%d\n",
> -		       iommu_present(&pci_bus_type) && dmar_platform_optin());
> +		       iommu_present(&pci_bus_type) &&
> +		       (dmar_platform_optin() || amd_ivrs_remap_support()));

Yikes.  No, the thunderbot code does not have any business poking into
either dmar_platform_optin or amd_ivrs_remap_support.  This needs
a proper abstration from the IOMMU code.