Re: [PATCH] iommu/dma: Setup iova_domain granule for IOMMU_DMA_MSI cookies

[Auger Eric]

Hi Nate,

On 16/05/2017 22:07, Nate Watterson wrote:
> 
> 
> 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!

Best Regards

Eric
> 
>>
>> Thanks
>>
>> Eric
>>
>>>
>>>>
>>>> Robin.
>>>>
>>>>> Fixes: a44e6657585b ("iommu/dma: Clean up MSI IOVA allocation")
>>>>> Signed-off-by: Nate Watterson <nwatters@xxxxxxxxxxxxxx>
>>>>> ---
>>>>>    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);
>>>>>
>>>>
>