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

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Message-ID: <64f72c46-75df-ce67-e81a-3b85cfe4c7d1@amd.com>
Date:   Fri, 19 May 2017 14:55:29 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 23/32] swiotlb: Add warnings for use of bounce buffers
 with SME

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@....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

>