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

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Message-ID: <90fe2111-42e5-ecb1-d0bd-10e06883ae5d@arm.com>
Date:   Thu, 13 Apr 2017 12:21:25 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Nate Watterson <nwatters@...eaurora.org>,
        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 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@...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);
>