Re: [PATCH] virtio_pci: limit Oracle DSC2-200 virtio-net to 48-bit DMA

[sashiko-bot@kernel.org]

> The virtio-net function of the AMD Pensando DSC2-200 (Elba) DPU, as
> shipped by Oracle (1af4:1041, subsystem 108e:1200), cannot DMA to
> arbitrary 64-bit bus addresses, and Oracle advises limiting it to 48
> bits. virtio_pci gives it a 64-bit mask, so its virtqueues stop
> completing requests once the IOMMU starts handing it IOVAs above 2^48.
> The card is used in OCI bare-metal shapes such as BM.Standard.E6.288.
> 
> On those AMD EPYC 9005 hosts the AMD IOMMU supports a 6-level v1 page
> table (EFR[HATS] = 2), so the aperture spans all 64 bits and the IOVA
> allocator, which works down from min(mask, aperture), returns addresses
> just below 2^64:
> 
>  - With iommu.forcedac=1, the first control virtqueue command never
>    completes and virtio_net hangs in probe.
> 
> [ ... ]
> 
> Cc: stable@vger.kernel.org # 6.5+
> Co-developed-by: Kyle McMartin <jkkm@meta.com>
> Signed-off-by: Kyle McMartin <jkkm@meta.com>
> Signed-off-by: Vlad Poenaru <vlad.wing@gmail.com>

Sashiko has reviewed this patch and found no issues.

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