Re: `AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y` causes AMDGPU to fail on Ryzen: amdgpu: SME is not compatible with RAVEN

[Alex Deucher <alexdeucher@gmail.com>]

On Mon, Oct 11, 2021 at 10:21 AM Paul Menzel <pmenzel@molgen.mpg.de> wrote:
>
> Dear Tom,
>
>
> Am 11.10.21 um 15:58 schrieb Tom Lendacky:
> > On 10/11/21 8:52 AM, Paul Menzel wrote:
>
> >> Am 11.10.21 um 15:27 schrieb Tom Lendacky:
> >>> On 10/11/21 8:11 AM, Borislav Petkov wrote:
> >>>> On Mon, Oct 11, 2021 at 03:05:33PM +0200, Paul Menzel wrote:
> >>>>> I think, the IOMMU is enabled on the MSI B350M MORTAR, but
> >>>>> otherwise, yes
> >>>>> this looks fine. The help text could also be updated to mention
> >>>>> problems
> >>>>> with AMD Raven devices.
> >>>>
> >>>> This is not only about Raven GPUs but, as Alex explained, pretty much
> >>>> about every device which doesn't support a 48 bit DMA mask. I'll expand
> >>>> that aspect in the changelog.
> >>>
> >>> In general, non-GPU devices that don't support a 48-bit DMA mask work
> >>> fine (assuming they have set their DMA mask appropriately). It really
> >>> depends on whether SWIOTLB will be able to satisfy the memory
> >>> requirements of the driver when the IOMMU is not enabled or in
> >>> passthrough mode. Since GPU devices need/use a lot of memory, that
> >>> becomes a problem.
> >>
> >> How can I check that?
> >
> > How can you check what? 32-bit DMA devices? GPUs? I need a bit more
> > information...
>
> How can I check, why MEM_ENCRYPT is not working on my device despite the
> IOMMU being enabled.

I think there are several potential problem cases:

1. Device is in passthrough mode in the IOMMU and the device has a
limited DMA mask.  This could be due to a hardware requirements (e.g.,
IOMMUv2 functionality) or a hardware/platform requirements (e.g., ACPI
IOMMU tables define passthrough for a specific device or memory
region).  This is the case for Raven.

2. Device driver bug (e.g., driver not using the DMA API properly)

Alex

>
>
> Kind regards,
>
> Paul