Date:   Tue, 16 May 2017 16:07:32 -0400
From:   Nate Watterson <nwatters@...eaurora.org>
To:     Auger Eric <eric.auger@...hat.com>,
        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



On 5/16/2017 3:55 PM, Auger Eric wrote:
> 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?

iommu/dma: Don't touch invalid iova_domain members

> 
> 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);
>>>>
>>>

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