From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: joro@8bytes.org, baolu.lu@linux.intel.com,
andreas.noever@gmail.com, michael.jamet@intel.com,
YehezkelShB@gmail.com, iommu@lists.linux-foundation.org,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
mario.limonciello@amd.com, hch@lst.de
Subject: Re: [PATCH v3 3/4] thunderbolt: Make iommu_dma_protection more accurate
Date: Tue, 5 Apr 2022 15:09:07 +0300 [thread overview]
Message-ID: <YkwxY59ACqFF9jer@lahna> (raw)
In-Reply-To: <b1f89ea2ad38221e0b75783357b9afb53087061d.1649089693.git.robin.murphy@arm.com>
On Tue, Apr 05, 2022 at 11:41:03AM +0100, Robin Murphy wrote:
> Between me trying to get rid of iommu_present() and Mario wanting to
> support the AMD equivalent of DMAR_PLATFORM_OPT_IN, scrutiny has shown
> that the iommu_dma_protection attribute is being far too optimistic.
> Even if an IOMMU might be present for some PCI segment in the system,
> that doesn't necessarily mean it provides translation for the device(s)
> we care about. Furthermore, all that DMAR_PLATFORM_OPT_IN really does
> is tell us that memory was protected before the kernel was loaded, and
> prevent the user from disabling the intel-iommu driver entirely. While
> that lets us assume kernel integrity, what matters for actual runtime
> DMA protection is whether we trust individual devices, based on the
> "external facing" property that we expect firmware to describe for
> Thunderbolt ports.
>
> It's proven challenging to determine the appropriate ports accurately
> given the variety of possible topologies, so while still not getting a
> perfect answer, by putting enough faith in firmware we can at least get
> a good bit closer. If we can see that any device near a Thunderbolt NHI
> has all the requisites for Kernel DMA Protection, chances are that it
> *is* a relevant port, but moreover that implies that firmware is playing
> the game overall, so we'll use that to assume that all Thunderbolt ports
> should be correctly marked and thus will end up fully protected.
>
> CC: Mario Limonciello <mario.limonciello@amd.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
next prev parent reply other threads:[~2022-04-05 21:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-05 10:41 [PATCH v3 0/4] thunderbolt: Make iommu_dma_protection more accurate Robin Murphy
2022-04-05 10:41 ` [PATCH v3 1/4] iommu: Introduce device_iommu_capable() Robin Murphy
2022-04-06 5:28 ` Christoph Hellwig
2022-04-06 10:32 ` Robin Murphy
2022-04-05 10:41 ` [PATCH v3 2/4] iommu: Add capability for pre-boot DMA protection Robin Murphy
2022-04-06 10:28 ` Lu Baolu
2022-04-05 10:41 ` [PATCH v3 3/4] thunderbolt: Make iommu_dma_protection more accurate Robin Murphy
2022-04-05 12:09 ` Mika Westerberg [this message]
2022-04-05 10:41 ` [PATCH v3 4/4] iommu/amd: Indicate whether DMA remap support is enabled Robin Murphy
2022-04-06 5:28 ` Christoph Hellwig
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