Date:   Fri, 17 Feb 2017 10:51:31 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.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>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Larry Woodman <lwoodman@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v4 19/28] swiotlb: Add warnings for use of bounce
 buffers with SME

On 2/17/2017 9:59 AM, Konrad Rzeszutek Wilk wrote:
> On Thu, Feb 16, 2017 at 09:46:19AM -0600, 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 87e816f..5a17f1b 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) ? true : false;
>>  }
>>
>> +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,
>> @@ -53,6 +58,12 @@ 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 10c5a17..130bef7 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
>> @@ -557,6 +558,11 @@ 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(dev,
>> +			 "SME is active, device will require DMA bounce buffers\n");
>
> You can make it one line. But I am wondering if you should use
> printk_ratelimit as this may fill the console up.

I thought the use of dma_set_mask() was mostly a one time probe/setup
thing so I didn't think we would get that many of these messages. If
dma_set_mask() is called much more often that that I can change this
to a printk_ratelimit().  I'll look into it further.

>
>> +
>>  	*dev->dma_mask = mask;
>>  	return 0;
>>  }
>> @@ -576,6 +582,11 @@ static inline int dma_set_coherent_mask(struct device *dev, u64 mask)
>>  {
>>  	if (!dma_supported(dev, mask))
>>  		return -EIO;
>> +
>> +	if (sme_active() && (mask < sme_dma_mask()))
>> +		dev_warn(dev,
>> +			 "SME is active, device will require DMA bounce buffers\n");
>
> Ditto.
>> +
>>  	dev->coherent_dma_mask = mask;
>>  	return 0;
>>  }
>> diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
>> index 14a7b9f..6829ff1 100644
>> --- a/include/linux/mem_encrypt.h
>> +++ b/include/linux/mem_encrypt.h
>> @@ -28,6 +28,12 @@ static inline bool sme_active(void)
>>  {
>>  	return false;
>>  }
>> +
>> +static inline u64 sme_dma_mask(void)
>> +{
>> +	return 0ULL;
>> +}
>> +
>>  #endif
>>
>>  #endif	/* CONFIG_AMD_MEM_ENCRYPT */
>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>> index c463067..aff9353 100644
>> --- a/lib/swiotlb.c
>> +++ b/lib/swiotlb.c
>> @@ -509,6 +509,9 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
>>  	if (no_iotlb_memory)
>>  		panic("Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer");
>>
>> +	WARN_ONCE(sme_active(),
>> +		  "SME is active and system is using DMA bounce buffers\n");
>
> How does that help?
>
> As in what can the user do with this?

It's meant just to notify the user about the condition. The user could
then decide to use an alternative device that supports a greater DMA
range (I can probably change it to a dev_warn_once() so that a device
is identified).  I would be nice if I could issue this message once per
device that experienced this.  I didn't see anything that would do
that, though.

Thanks,
Tom

>> +
>>  	mask = dma_get_seg_boundary(hwdev);
>>
>>  	tbl_dma_addr &= mask;
>>

Powered by blists - more mailing lists