[Bug 211117] dma_mmap_coherent() - garbage sound output with mem_encrypt on Ryzen platform

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=211117

thomas.lendacky@amd.com changed:

           What    |Removed                     |Added
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                 CC|                            |thomas.lendacky@amd.com

--- Comment #17 from thomas.lendacky@amd.com ---
This sounds like a mismatch between the encryption bit in the kernel and the
encryption bit in userspace. It looks like that should be taken care of by the
dma_pgprot() call in dma_mmap_attrs() or in iommu_dma_mmap(). But maybe the
force_dma_unencrypted() in arch/x86/mm/mem_encrypt.c needs to understand if the
IOMMU is doing the mapping. Since, even if the device doesn't support 48-bit or
higher DMA, it will still done encrypted because of the IOMMU. I don't see any
dmesg output, is the IOMMU enabled? What happens if you do iommu=pt on the
kernel command line?

Alternatively, if you want memory encryption for your bare-metal system, you
can see if the BIOS supports TSME (Transparent SME). Then you can remove
mem_encrypt=on or add mem_encrypt=off (if enabled by default), and still get
memory encryption.

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