Re: [PATCH v5 23/32] swiotlb: Add warnings for use of bounce buffers with SME

Tom Lendacky
2017-05-19T19:55:43Z

On 5/16/2017 9:52 AM, Borislav Petkov wrote:
> On Tue, Apr 18, 2017 at 04:20:19PM -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.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>> arch/x86/include/asm/mem_encrypt.h | 11 +++++++++++
>> include/linux/dma-mapping.h | 11 +++++++++++
>> include/linux/mem_encrypt.h | 6 ++++++
>> lib/swiotlb.c | 3 +++
>> 4 files changed, 31 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
>> index 0637b4b..b406df2 100644
>> --- a/arch/x86/include/asm/mem_encrypt.h
>> +++ b/arch/x86/include/asm/mem_encrypt.h
>> @@ -26,6 +26,11 @@ static inline bool sme_active(void)
>> return !!sme_me_mask;
>> }
>>
>> +static inline u64 sme_dma_mask(void)
>> +{
>> + return ((u64)sme_me_mask << 1) - 1;
>> +}
>> +
>> void __init sme_early_encrypt(resource_size_t paddr,
>> unsigned long size);
>> void __init sme_early_decrypt(resource_size_t paddr,
>> @@ -50,6 +55,12 @@ static inline bool sme_active(void)
>> {
>> return false;
>> }
>> +
>> +static inline u64 sme_dma_mask(void)
>> +{
>> + return 0ULL;
>> +}
>> +
>> #endif
>>
>> static inline void __init sme_early_encrypt(resource_size_t paddr,
>> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
>> index 0977317..f825870 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;
>> +
>> + if (sme_active() && (mask < sme_dma_mask()))
>> + dev_warn_ratelimited(dev,
>> + "SME is active, device will require DMA bounce buffers\n");
>
> Bah, no need to break that line - just let it stick out. Ditto for the
> others.

Ok.

Thanks,
Tom

>