On 01/02/2019 16:16, Christoph Hellwig wrote:
On Fri, Feb 01, 2019 at 03:24:45PM +0000, Robin Murphy wrote:
On 14/01/2019 09:41, Christoph Hellwig wrote:
Directly iterating over the pages makes the code a bit simpler and
prepares for the following changes.
It also defeats the whole purpose of __iommu_dma_alloc_pages(), so I'm not
really buying the simplification angle - you've *seen* that code, right? ;)
How does it defeat the purpose of __iommu_dma_alloc_pages?
Because if iommu_map() only gets called at PAGE_SIZE granularity, then
the IOMMU PTEs will be created at PAGE_SIZE (or smaller) granularity, so
any effort to get higher-order allocations matching larger IOMMU block
sizes is wasted, and we may as well have just done this:
for (i = 0; i < count; i++) {
struct page *page = alloc_page(gfp);
...
iommu_map(..., page_to_phys(page), PAGE_SIZE, ...);
}
Really, it's a shame we have to split huge pages for the CPU remap,
since in the common case the CPU MMU will have a matching block size,
but IIRC there was something in vmap() or thereabouts that explicitly
chokes on them.
Robin.
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
