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

[Shanker Donthineni <shankerd@codeaurora.org>]

Hi Robin,

I tested your changes and the device pass-through feature works fine on QDF2400 server platform. Maybe Nate comments on the patch contents but it fixes the problem.


@@ -317,13 +317,13 @@ 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,
@@ -538,11 +538,14 @@ 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);
+       }


On 04/13/2017 06:21 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:
>
> ----->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 ;)
>
> Robin.
>
>> Fixes: a44e6657585b ("iommu/dma: Clean up MSI IOVA allocation")
>> Signed-off-by: Nate Watterson <nwatters@codeaurora.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);
>>

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.