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[RFC PATCH 1/3] iommu: Add support for out of band flushing

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  [RFC PATCH 1/3] iommu: Add support for out of band flushing Tomasz Figa <tfiga@chromium.org> - 2015-09-29 07:30 +0200
    Re: [RFC PATCH 1/3] iommu: Add support for out of band flushing Thierry Reding <thierry.reding@gmail.com> - 2015-09-29 11:40 +0200
      Re: [RFC PATCH 1/3] iommu: Add support for out of band flushing Tomasz Figa <tfiga@chromium.org> - 2015-09-29 14:00 +0200

#1234721 — [RFC PATCH 1/3] iommu: Add support for out of band flushing

This patch adds a new "flush" callback to iommu_ops, which is supposed
to perform any necessary flushes within given IOMMU domain to make any
changes to mappings of given area [iova; iova + size) be reflected to
IOMMU clients.

The purpose is to let IOMMU drivers skip page-by-page flushes and
replace it with one flush of full address range on devices which support
it.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
---
 drivers/iommu/iommu.c | 33 ++++++++++++++++++++++++++++++---
 include/linux/iommu.h |  2 ++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 049df49..d6bb8fe 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1286,8 +1286,15 @@ static size_t iommu_pgsize(struct iommu_domain *domain,
 	return pgsize;
 }
 
-int iommu_map(struct iommu_domain *domain, unsigned long iova,
-	      phys_addr_t paddr, size_t size, int prot)
+static void iommu_flush(struct iommu_domain *domain, unsigned long iova,
+			size_t size)
+{
+	if (domain->ops->flush)
+		domain->ops->flush(domain, iova, size);
+}
+
+static int __iommu_map(struct iommu_domain *domain, unsigned long iova,
+		       phys_addr_t paddr, size_t size, int prot)
 {
 	unsigned long orig_iova = iova;
 	unsigned int min_pagesz;
@@ -1340,6 +1347,20 @@ int iommu_map(struct iommu_domain *domain, unsigned long iova,
 
 	return ret;
 }
+
+int iommu_map(struct iommu_domain *domain, unsigned long iova,
+	      phys_addr_t paddr, size_t size, int prot)
+{
+	int ret;
+
+	ret = __iommu_map(domain, iova, paddr, size, prot);
+	if (ret)
+		return ret;
+
+	iommu_flush(domain, iova, size);
+
+	return 0;
+}
 EXPORT_SYMBOL_GPL(iommu_map);
 
 size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
@@ -1389,6 +1410,7 @@ size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
 		unmapped += unmapped_page;
 	}
 
+	iommu_flush(domain, orig_iova, unmapped);
 	trace_unmap(orig_iova, size, unmapped);
 	return unmapped;
 }
@@ -1419,19 +1441,24 @@ size_t default_iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
 		if (!IS_ALIGNED(s->offset, min_pagesz))
 			goto out_err;
 
-		ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
+		ret = __iommu_map(domain, iova + mapped, phys, s->length, prot);
 		if (ret)
 			goto out_err;
 
 		mapped += s->length;
 	}
 
+	iommu_flush(domain, iova, mapped);
+
 	return mapped;
 
 out_err:
 	/* undo mappings already done */
 	iommu_unmap(domain, iova, mapped);
 
+	/* flush in case part of our mapping already got cached */
+	iommu_flush(domain, iova, mapped);
+
 	return 0;
 
 }
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index f9c1b6d..18e59a9 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -164,6 +164,8 @@ struct iommu_ops {
 		     size_t size);
 	size_t (*map_sg)(struct iommu_domain *domain, unsigned long iova,
 			 struct scatterlist *sg, unsigned int nents, int prot);
+	void (*flush)(struct iommu_domain *domain, unsigned long iova,
+		      size_t size);
 	phys_addr_t (*iova_to_phys)(struct iommu_domain *domain, dma_addr_t iova);
 	int (*add_device)(struct device *dev);
 	void (*remove_device)(struct device *dev);
-- 
2.6.0.rc2.230.g3dd15c0

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#1234913

[Multipart message — attachments visible in raw view] — view raw

On Tue, Sep 29, 2015 at 02:25:24PM +0900, Tomasz Figa wrote:
> This patch adds a new "flush" callback to iommu_ops, which is supposed
> to perform any necessary flushes within given IOMMU domain to make any
> changes to mappings of given area [iova; iova + size) be reflected to
> IOMMU clients.
> 
> The purpose is to let IOMMU drivers skip page-by-page flushes and
> replace it with one flush of full address range on devices which support
> it.
> 
> Signed-off-by: Tomasz Figa <tfiga@chromium.org>
> ---
>  drivers/iommu/iommu.c | 33 ++++++++++++++++++++++++++++++---
>  include/linux/iommu.h |  2 ++
>  2 files changed, 32 insertions(+), 3 deletions(-)

I seem to remember that Rob Clark had proposed something like this back
before it was decided to introduce the ->map_sg() callback instead. I
can't find a reference to the discussion, so perhaps I'm misremembering
but adding Rob Clark in case he has any recollection of why the outcome
was what it was.

> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
[...]
> @@ -1389,6 +1410,7 @@ size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
>  		unmapped += unmapped_page;
>  	}
>  
> +	iommu_flush(domain, orig_iova, unmapped);
>  	trace_unmap(orig_iova, size, unmapped);
>  	return unmapped;
>  }
> @@ -1419,19 +1441,24 @@ size_t default_iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
>  		if (!IS_ALIGNED(s->offset, min_pagesz))
>  			goto out_err;
>  
> -		ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
> +		ret = __iommu_map(domain, iova + mapped, phys, s->length, prot);
>  		if (ret)
>  			goto out_err;
>  
>  		mapped += s->length;
>  	}
>  
> +	iommu_flush(domain, iova, mapped);
> +
>  	return mapped;
>  
>  out_err:
>  	/* undo mappings already done */
>  	iommu_unmap(domain, iova, mapped);
>  
> +	/* flush in case part of our mapping already got cached */
> +	iommu_flush(domain, iova, mapped);
> +
>  	return 0;
>  
>  }

iommu_unmap() already does an iommu_flush(), so why flush again after
iommu_unmap()?

Thierry

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#1234996

On Tue, Sep 29, 2015 at 6:32 PM, Thierry Reding
<thierry.reding@gmail.com> wrote:
> On Tue, Sep 29, 2015 at 02:25:24PM +0900, Tomasz Figa wrote:
>> This patch adds a new "flush" callback to iommu_ops, which is supposed
>> to perform any necessary flushes within given IOMMU domain to make any
>> changes to mappings of given area [iova; iova + size) be reflected to
>> IOMMU clients.
>>
>> The purpose is to let IOMMU drivers skip page-by-page flushes and
>> replace it with one flush of full address range on devices which support
>> it.
>>
>> Signed-off-by: Tomasz Figa <tfiga@chromium.org>
>> ---
>>  drivers/iommu/iommu.c | 33 ++++++++++++++++++++++++++++++---
>>  include/linux/iommu.h |  2 ++
>>  2 files changed, 32 insertions(+), 3 deletions(-)
>
> I seem to remember that Rob Clark had proposed something like this back
> before it was decided to introduce the ->map_sg() callback instead. I
> can't find a reference to the discussion, so perhaps I'm misremembering
> but adding Rob Clark in case he has any recollection of why the outcome
> was what it was.

Oops, I was supposed to add Rob, but forgot in the end. Thanks for remembering.

>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> [...]
>> @@ -1389,6 +1410,7 @@ size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
>>               unmapped += unmapped_page;
>>       }
>>
>> +     iommu_flush(domain, orig_iova, unmapped);
>>       trace_unmap(orig_iova, size, unmapped);
>>       return unmapped;
>>  }
>> @@ -1419,19 +1441,24 @@ size_t default_iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
>>               if (!IS_ALIGNED(s->offset, min_pagesz))
>>                       goto out_err;
>>
>> -             ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
>> +             ret = __iommu_map(domain, iova + mapped, phys, s->length, prot);
>>               if (ret)
>>                       goto out_err;
>>
>>               mapped += s->length;
>>       }
>>
>> +     iommu_flush(domain, iova, mapped);
>> +
>>       return mapped;
>>
>>  out_err:
>>       /* undo mappings already done */
>>       iommu_unmap(domain, iova, mapped);
>>
>> +     /* flush in case part of our mapping already got cached */
>> +     iommu_flush(domain, iova, mapped);
>> +
>>       return 0;
>>
>>  }
>
> iommu_unmap() already does an iommu_flush(), so why flush again after
> iommu_unmap()?

Right, my mistake. This should be removed. Thanks for catching.

Best regards,
Tomasz
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