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

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Date:   Tue, 15 Mar 2022 16:54:08 +0000
From:   "Limonciello, Mario" <Mario.Limonciello@....com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Joerg Roedel <joro@...tes.org>,
        "Suthikulpanit, Suravee" <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

[Public]


> 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.

To make sure I follow your ask - it's to make a new generic iommu function
That would check dmar/ivrs, and switch out thunderbolt domain.c to use the
symbol?

I'm happy to rework that if that is what you want.
Do you have a preferred proposed function name for that?