linux-kernel - Re: [PATCH 2/2] iommu/dma: Avoid SAC address trick for PCIe devices

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Date:   Wed, 22 Jul 2020 14:48:55 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     hch@....de, iommu@...ts.linux-foundation.org,
        jonathan.lemon@...il.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        dwmw2@...radead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] iommu/dma: Avoid SAC address trick for PCIe devices

On Tue, Jul 14, 2020 at 12:42:36PM +0100, Robin Murphy wrote:
> Oh bother - yes, this could have been masking all manner of bugs. That
> system will presumably also break if you managed to exhaust the 32-bit IOVA
> space such that the allocator moved up to the higher range anyway, or if you
> passed the XHCI through to a VM with a sufficiently wacky GPA layout, but I
> guess those are cases that simply nobody's run into yet.
> 
> Does the firmware actually report any upper address constraint such that
> Sebastian's IVRS aperture patches might help?

No, it doesn't. I am not sure what the best way is to get these issues
found and fixed. I doubt they will be getting fixed when the allocation
pattern isn't changed, maybe we can put your changes behind a config
variable and start testing/reporting bugs/etc.

Regards,

	Joerg