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From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: joro@8bytes.org, baolu.lu@linux.intel.com,
	andreas.noever@gmail.com, michael.jamet@intel.com,
	mika.westerberg@linux.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 v2 2/2] thunderbolt: Make iommu_dma_protection more accurate
Date: Tue, 22 Mar 2022 10:16:26 +0100	[thread overview]
Message-ID: <20220322091626.GB27069@lst.de> (raw)
In-Reply-To: <0dd14883930c9f55ace22162e23765a37d91a057.1647624084.git.robin.murphy@arm.com>

On Fri, Mar 18, 2022 at 05:42:58PM +0000, 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>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Looks sensible to me:

Acked-by: Christoph Hellwig <hch@lst.de>

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: michael.jamet@intel.com, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, YehezkelShB@gmail.com,
	iommu@lists.linux-foundation.org, mario.limonciello@amd.com,
	andreas.noever@gmail.com, mika.westerberg@linux.intel.com,
	hch@lst.de
Subject: Re: [PATCH v2 2/2] thunderbolt: Make iommu_dma_protection more accurate
Date: Tue, 22 Mar 2022 10:16:26 +0100	[thread overview]
Message-ID: <20220322091626.GB27069@lst.de> (raw)
In-Reply-To: <0dd14883930c9f55ace22162e23765a37d91a057.1647624084.git.robin.murphy@arm.com>

On Fri, Mar 18, 2022 at 05:42:58PM +0000, 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>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Looks sensible to me:

Acked-by: Christoph Hellwig <hch@lst.de>
_______________________________________________
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iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  parent reply	other threads:[~2022-03-22  9:16 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-18 17:42 [PATCH v2 0/2] thunderbolt: Make iommu_dma_protection more accurate Robin Murphy
2022-03-18 17:42 ` Robin Murphy
2022-03-18 17:42 ` [PATCH v2 1/2] iommu: Add capability for pre-boot DMA protection Robin Murphy
2022-03-18 17:42   ` Robin Murphy
2022-03-22  9:14   ` Christoph Hellwig
2022-03-22  9:14     ` Christoph Hellwig
2022-03-22  9:53     ` Robin Murphy
2022-03-22  9:53       ` Robin Murphy
2022-03-18 17:42 ` [PATCH v2 2/2] thunderbolt: Make iommu_dma_protection more accurate Robin Murphy
2022-03-18 17:42   ` Robin Murphy
2022-03-18 22:29   ` Limonciello, Mario
2022-03-18 22:29     ` Limonciello, Mario via iommu
2022-03-21 10:58     ` mika.westerberg
2022-03-21 10:58       ` mika.westerberg
2022-03-21 11:11       ` Robin Murphy
2022-03-21 11:11         ` Robin Murphy
2022-03-21 13:21         ` Limonciello, Mario
2022-03-21 13:21           ` Limonciello, Mario via iommu
2022-03-22  9:16   ` Christoph Hellwig [this message]
2022-03-22  9:16     ` Christoph Hellwig
2022-03-22 11:41   ` Mika Westerberg
2022-03-22 11:41     ` Mika Westerberg
2022-03-22 14:40     ` Robin Murphy
2022-03-22 14:40       ` Robin Murphy

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