Re: [RFC Part1 PATCH v3 12/17] x86/mm: DMA support for SEV memory encryption

Borislav Petkov
2017-08-07T03:48:20Z

On Mon, Jul 24, 2017 at 02:07:52PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
>
> DMA access to memory mapped as encrypted while SEV is active can not be
> encrypted during device write or decrypted during device read.

Yeah, definitely rewrite that sentence.

> In order
> for DMA to properly work when SEV is active, the SWIOTLB bounce buffers
> must be used.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/mm/mem_encrypt.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++
> lib/swiotlb.c | 5 +--
> 2 files changed, 89 insertions(+), 2 deletions

...

> @@ -202,6 +280,14 @@ void __init mem_encrypt_init(void)
> /* Call into SWIOTLB to update the SWIOTLB DMA buffers */
> swiotlb_update_mem_attributes();
>
> + /*
> + * With SEV, DMA operations cannot use encryption. New DMA ops
> + * are required in order to mark the DMA areas as decrypted or
> + * to use bounce buffers.
> + */
> + if (sev_active())
> + dma_ops = &sme_dma_ops;

Well, we do differentiate between SME and SEV and the check is
sev_active but the ops are called sme_dma_ops. Call them sev_dma_ops
instead for less confusion.

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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