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SubjectRe: [RFC PATCH v3 13/20] x86: DMA support for memory encryption
On Tue, Nov 15, 2016 at 12:29:35PM -0600, Tom Lendacky wrote:
> On 11/15/2016 9:16 AM, Michael S. Tsirkin wrote:
> > On Wed, Nov 09, 2016 at 06:37:23PM -0600, Tom Lendacky wrote:
> >> Since DMA addresses will effectively look like 48-bit addresses when the
> >> memory encryption mask is set, SWIOTLB is needed if the DMA mask of the
> >> device performing the DMA does not support 48-bits. SWIOTLB will be
> >> initialized to create un-encrypted bounce buffers for use by these devices.
> >>
> >> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> >> ---
> >> arch/x86/include/asm/dma-mapping.h | 5 ++-
> >> arch/x86/include/asm/mem_encrypt.h | 5 +++
> >> arch/x86/kernel/pci-dma.c | 11 ++++---
> >> arch/x86/kernel/pci-nommu.c | 2 +
> >> arch/x86/kernel/pci-swiotlb.c | 8 ++++-
> >> arch/x86/mm/mem_encrypt.c | 17 +++++++++++
> >> include/linux/swiotlb.h | 1 +
> >> init/main.c | 13 ++++++++
> >> lib/swiotlb.c | 58 +++++++++++++++++++++++++++++++-----
> >> 9 files changed, 103 insertions(+), 17 deletions(-)
> >>
> >> diff --git a/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h
> >> index 4446162..c9cdcae 100644
> >> --- a/arch/x86/include/asm/dma-mapping.h
> >> +++ b/arch/x86/include/asm/dma-mapping.h
>
> ..SNIP...
>
> >>
> >> +/*
> >> + * If memory encryption is active, the DMA address for an encrypted page may
> >> + * be beyond the range of the device. If bounce buffers are required be sure
> >> + * that they are not on an encrypted page. This should be called before the
> >> + * iotlb area is used.
> >
> > Makes sense, but I think at least a dmesg warning here
> > might be a good idea.
>
> Good idea. Should it be a warning when it is first being set up or
> a warning the first time the bounce buffers need to be used. Or maybe
> both?
>
> >
> > A boot flag that says "don't enable devices that don't support
> > encryption" might be a good idea, too, since most people
> > don't read dmesg output and won't notice the message.
>
> I'll look into this. It might be something that can be checked as
> part of the device setting its DMA mask or the first time a DMA
> API is used if the device doesn't explicitly set its mask.
>
> Thanks,
> Tom
>
> >

I think setup time is nicer if it's possible.

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