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

[Tom Lendacky]

On 8/6/2017 10:48 PM, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 02:07:52PM -0500, Brijesh Singh wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> >
> > 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.

Heh, yup.

> > 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@xxxxxxx>
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > ---
> >   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.

Yup, will do.

Thanks,
Tom

>