On 6/21/2017 5:50 AM, Borislav Petkov wrote:
> On Fri, Jun 16, 2017 at 01:54:36PM -0500, Tom Lendacky wrote:
>> Add warnings to let the user know when bounce buffers are being used for
>> DMA when SME is active. Since the bounce buffers are not in encrypted
>> memory, these notifications are to allow the user to determine some
>> appropriate action - if necessary. Actions can range from utilizing an
>> IOMMU, replacing the device with another device that can support 64-bit
>> DMA, ignoring the message if the device isn't used much, etc.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
>> ---
>> include/linux/dma-mapping.h | 11 +++++++++++
>> include/linux/mem_encrypt.h | 8 ++++++++
>> lib/swiotlb.c | 3 +++
>> 3 files changed, 22 insertions(+)
>>
>> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
>> index 4f3eece..ee2307e 100644
>> --- a/include/linux/dma-mapping.h
>> +++ b/include/linux/dma-mapping.h
>> @@ -10,6 +10,7 @@
>> #include <linux/scatterlist.h>
>> #include <linux/kmemcheck.h>
>> #include <linux/bug.h>
>> +#include <linux/mem_encrypt.h>
>>
>> /**
>> * List of possible attributes associated with a DMA mapping. The semantics
>> @@ -577,6 +578,11 @@ static inline int dma_set_mask(struct device *dev, u64 mask)
>>
>> if (!dev->dma_mask || !dma_supported(dev, mask))
>> return -EIO;
>> +
>> + /* Since mask is unsigned, this can only be true if SME is active */
>> + if (mask < sme_dma_mask())
>> + dev_warn(dev, "SME is active, device will require DMA bounce buffers\n");
>> +
>> *dev->dma_mask = mask;
>> return 0;
>> }
>> @@ -596,6 +602,11 @@ static inline int dma_set_coherent_mask(struct device *dev, u64 mask)
>> {
>> if (!dma_supported(dev, mask))
>> return -EIO;
>> +
>> + /* Since mask is unsigned, this can only be true if SME is active */
>> + if (mask < sme_dma_mask())
>> + dev_warn(dev, "SME is active, device will require DMA bounce buffers\n");
>
> Looks to me like those two checks above need to be a:
>
> void sme_check_mask(struct device *dev, u64 mask)
> {
> if (!sme_me_mask)
> return;
>
> /* Since mask is unsigned, this can only be true if SME is active */
> if (mask < (((u64)sme_me_mask << 1) - 1))
> dev_warn(dev, "SME is active, device will require DMA bounce buffers\n");
> }
>
> which gets called and sme_dma_mask() is not really needed.
Makes a lot of sense, I'll update the patch.
Thanks,
Tom
>
