linux-kernel - Re: [PATCH] iommu/dma: Setup iova_domain granule for IOMMU_DMA

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Date:   Tue, 16 May 2017 21:55:19 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Nate Watterson <nwatters@...eaurora.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     shankerd@...eaurora.org
Subject: Re: [PATCH] iommu/dma: Setup iova_domain granule for IOMMU_DMA_MSI
 cookies

Hi,

On 13/04/2017 21:38, Nate Watterson wrote:
> Hi Robin,
> 
> On 4/13/2017 7:21 AM, Robin Murphy wrote:
>> Hi Nate,
>>
>> On 13/04/17 09:55, Nate Watterson wrote:
>>> Currently, the __iommu_dma_{map/free} functions call iova_{offset/align}
>>> making them unsuitable for use with iommu_domains having an
>>> IOMMU_DMA_MSI
>>> cookie since the cookie's iova_domain member, iovad, is uninitialized.
>>>
>>> Now that iommu_dma_get_msi_page() calls __iommu_dma_map() regardless
>>> of cookie type, failures are being seen when mapping MSI target
>>> addresses for devices attached to UNMANAGED domains. To work around
>>> this issue, the iova_domain granule for IOMMU_DMA_MSI cookies is
>>> initialized to the value returned by cookie_msi_granule().
>>
>> Oh bum. Thanks for the report.
>>
>> However, I really don't like bodging around it with deliberate undefined
>> behaviour. Fixing things properly doesn't seem too hard:
> 
> I was not especially please with my solution, but I wanted to avoid
> potentially missing any other spots in the code where granule was
> used uninitialized. The compile time check made me feel a little
> less dirty about innappropriately using the iova_domain with MSI
> cookies.
> 
>>
>> ----->8-----
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index 8348f366ddd1..62618e77bedc 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -396,13 +396,13 @@ static void iommu_dma_free_iova(struct
>> iommu_dma_cookie *cookie,
>>                  dma_addr_t iova, size_t size)
>>   {
>>          struct iova_domain *iovad = &cookie->iovad;
>> -       unsigned long shift = iova_shift(iovad);
>>
>>          /* The MSI case is only ever cleaning up its most recent
>> allocation */
>>          if (cookie->type == IOMMU_DMA_MSI_COOKIE)
>>                  cookie->msi_iova -= size;
>>          else
>> -               free_iova_fast(iovad, iova >> shift, size >> shift);
>> +               free_iova_fast(iovad, iova_pfn(iovad, iova),
>> +                               size >> iova_shift(iovad));
>>   }
>>
>>   static void __iommu_dma_unmap(struct iommu_domain *domain, dma_addr_t
>> dma_addr,
>> @@ -617,11 +617,14 @@ static dma_addr_t __iommu_dma_map(struct device
>> *dev, phys_addr_t phys,
>>   {
>>          struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
>>          struct iommu_dma_cookie *cookie = domain->iova_cookie;
>> -       struct iova_domain *iovad = &cookie->iovad;
>> -       size_t iova_off = iova_offset(iovad, phys);
>> +       size_t iova_off = 0;
>>          dma_addr_t iova;
>>
>> -       size = iova_align(iovad, size + iova_off);
>> +       if (cookie->type == IOMMU_DMA_IOVA_COOKIE) {
>> +               iova_off = iova_offset(&cookie->iovad, phys);
>> +               size = iova_align(&cookie->iovad, size + iova_off);
>> +       }
>> +
>>          iova = iommu_dma_alloc_iova(domain, size, dma_get_mask(dev),
>> dev);
>>          if (!iova)
>>                  return DMA_ERROR_CODE;
>> -----8<-----
>>
>> Untested, and you'll probably want to double-check it anyway given that
>> the original oversight was mine in the first place ;)
> 
> This looks good to me. As Shanker has already mentioned, it does fix the
> faults we were previously seeing with direct device assignment. I also
> verified that there aren't any other obvious cases of a granule == 0
> being used in the dma_iommu code by adding BUG_ON(!iovad->granule) to
> iova_{mask/align/offset/...} and running a variety of tests without
> issue.
> 
> Are you going to post the patch?

I also noticed PCIe passthrough/ARM is broken for me with 4.12-r1. I
tested Robin's patch as well, on Cavium ThunderX, and this fixes the
faults I have seen.

Has anyone sent a formal patch?

Thanks

Eric

> 
>>
>> Robin.
>>
>>> Fixes: a44e6657585b ("iommu/dma: Clean up MSI IOVA allocation")
>>> Signed-off-by: Nate Watterson <nwatters@...eaurora.org>
>>> ---
>>>   drivers/iommu/dma-iommu.c | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>>>
>>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>>> index 8348f366..d7b0816 100644
>>> --- a/drivers/iommu/dma-iommu.c
>>> +++ b/drivers/iommu/dma-iommu.c
>>> @@ -127,6 +127,16 @@ int iommu_get_msi_cookie(struct iommu_domain
>>> *domain, dma_addr_t base)
>>>         cookie->msi_iova = base;
>>>       domain->iova_cookie = cookie;
>>> +
>>> +    /*
>>> +     * Setup granule for compatibility with __iommu_dma_{alloc/free}
>>> and
>>> +     * add a compile time check to ensure that writing granule won't
>>> +     * clobber msi_iova.
>>> +     */
>>> +    cookie->iovad.granule = cookie_msi_granule(cookie);
>>> +    BUILD_BUG_ON(offsetof(struct iova_domain, granule) <
>>> +            sizeof(cookie->msi_iova));
>>> +
>>>       return 0;
>>>   }
>>>   EXPORT_SYMBOL(iommu_get_msi_cookie);
>>>
>>