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SubjectRe: [PATCH v7 2/6] iommu/dma: Add support for non-strict mode
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On 2018-09-18 6:10 PM, Will Deacon wrote:
> Hi Robin,
>
> On Fri, Sep 14, 2018 at 03:30:20PM +0100, Robin Murphy wrote:
>> From: Zhen Lei <thunder.leizhen@huawei.com>
>>
>> 1. Save the related domain pointer in struct iommu_dma_cookie, make iovad
>> capable call domain->ops->flush_iotlb_all to flush TLB.
>> 2. During the iommu domain initialization phase, base on domain->non_strict
>> field to check whether non-strict mode is supported or not. If so, call
>> init_iova_flush_queue to register iovad->flush_cb callback.
>> 3. All unmap(contains iova-free) APIs will finally invoke __iommu_dma_unmap
>> -->iommu_dma_free_iova. If the domain is non-strict, call queue_iova to
>> put off iova freeing, and omit iommu_tlb_sync operation.
>
> Hmm, this is basically just a commentary on the code. Please could you write
> it more in terms of the problem that's being solved?

Sure - I intentionally kept a light touch when it came to the
documentation and commit messages in this rework (other than patch #1
where I eventually remembered the original reasoning and that it wasn't
a bug). If we're more-or-less happy with the shape of the technical side
I'll make sure to take a final pass through v8 to tidy up all the prose.

>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> [rm: convert raw boolean to domain attribute]
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>> drivers/iommu/dma-iommu.c | 29 ++++++++++++++++++++++++++++-
>> include/linux/iommu.h | 1 +
>> 2 files changed, 29 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index 511ff9a1d6d9..092e6926dc3c 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -55,6 +55,9 @@ struct iommu_dma_cookie {
>> };
>> struct list_head msi_page_list;
>> spinlock_t msi_lock;
>> +
>> + /* Only be assigned in non-strict mode, otherwise it's NULL */
>> + struct iommu_domain *domain;
>> };
>>
>> static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
>> @@ -257,6 +260,17 @@ static int iova_reserve_iommu_regions(struct device *dev,
>> return ret;
>> }
>>
>> +static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
>> +{
>> + struct iommu_dma_cookie *cookie;
>> + struct iommu_domain *domain;
>> +
>> + cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
>> + domain = cookie->domain;
>> +
>> + domain->ops->flush_iotlb_all(domain);
>
> Can we rely on this function pointer being non-NULL? I think it would
> be better to call iommu_flush_tlb_all(cookie->domain) instead.

Yeah, that's deliberate - in fact got as far as writing that change,
then undid it as I realised that although the attribute conversion got
rid of the explicit ops->flush_iotlb_all check, it still makes zero
sense for an IOMMU driver to claim to support the flush queue attribute
without also providing the relevant callback, so I do actually want this
to blow up rather than silently do nothing if that assumption isn't met.

>> +}
>> +
>> /**
>> * iommu_dma_init_domain - Initialise a DMA mapping domain
>> * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
>> @@ -275,6 +289,7 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>> struct iommu_dma_cookie *cookie = domain->iova_cookie;
>> struct iova_domain *iovad = &cookie->iovad;
>> unsigned long order, base_pfn, end_pfn;
>> + int attr = 1;
>
> Do we actually need to initialise this?

Oops, no, that's a left-over from the turned-out-messier-that-I-thought
v6 implementation.

Thanks,
Robin.

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