On Mon, Oct 28, 2024 at 08:22:52AM +0200, Leon Romanovsky wrote:
> On Mon, Oct 28, 2024 at 10:00:25AM +0800, Baolu Lu wrote:
> > On 2024/10/27 22:21, Leon Romanovsky wrote:
> > > +/**
> > > + * dma_iova_sync - Sync IOTLB
> > > + * @dev: DMA device
> > > + * @state: IOVA state
> > > + * @offset: offset into the IOVA state to sync
> > > + * @size: size of the buffer
> > > + * @ret: return value from the last IOVA operation
> > > + *
> > > + * Sync IOTLB for the given IOVA state. This function should be called on
> > > + * the IOVA-contigous range created by one ore more dma_iova_link() calls
> > > + * to sync the IOTLB.
> > > + */
> > > +int dma_iova_sync(struct device *dev, struct dma_iova_state *state,
> > > + size_t offset, size_t size, int ret)
> > > +{
> > > + struct iommu_domain *domain = iommu_get_dma_domain(dev);
> > > + struct iommu_dma_cookie *cookie = domain->iova_cookie;
> > > + struct iova_domain *iovad = &cookie->iovad;
> > > + dma_addr_t addr = state->addr + offset;
> > > + size_t iova_start_pad = iova_offset(iovad, addr);
> > > +
> > > + addr -= iova_start_pad;
> > > + size = iova_align(iovad, size + iova_start_pad);
> > > +
> > > + if (!ret)
> > > + ret = iommu_sync_map(domain, addr, size);
> > > + if (ret)
> > > + iommu_unmap(domain, addr, size);
> >
> > It appears strange that mapping is not done in this helper, but
> > unmapping is added in the failure path. Perhaps I overlooked anything?
>
> Like iommu_sync_map() is performed on whole continuous range, the iommu_unmap()
> should be done on the same range. So, technically you can unmap only part of
> the range which called to dma_iova_link() and failed, but you will need
> to make sure that iommu_sync_map() is still called for "successful" part of
> iommu_map().
>
> In that case, you will need to undo everything anyway and it means that
> you will call to iommu_unmap() on the successful part of the range
> anyway.
>
> dma_iova_sync() is single operation for the whole range and
> iommu_unmap() too, so they are bound together.
>
> > To my understanding, it should like below:
> >
> > return iommu_sync_map(domain, addr, size);
> >
> > In the drivers that make use of this interface should do something like
> > below:
> >
> > ret = dma_iova_sync(...);
> > if (ret)
> > dma_iova_destroy(...)
>
> It is actually what is happening in the code, but in less direct way due
> to unwinding of the code.
After more thoughts on the topic, I think that it will be better to make
this dma_iova_sync() less cryptic and more direct. I will change it to be
as below in my next version:
1972 int dma_iova_sync(struct device *dev, struct dma_iova_state *state,
1973 size_t offset, size_t size)
1974 {
1975 struct iommu_domain *domain = iommu_get_dma_domain(dev);
1976 struct iommu_dma_cookie *cookie = domain->iova_cookie;
1977 struct iova_domain *iovad = &cookie->iovad;
1978 dma_addr_t addr = state->addr + offset;
1979 size_t iova_start_pad = iova_offset(iovad, addr);
1980
1981 return iommu_sync_map(domain, addr - iova_start_pad,
1982 iova_align(iovad, size + iova_start_pad));
1983 }
1984 EXPORT_SYMBOL_GPL(dma_iova_sync);
Thanks
