On Thu, May 18, 2023, Yan Zhao wrote: > On Wed, May 17, 2023 at 07:50:26AM -0700, Sean Christopherson wrote: > > On Tue, May 16, 2023, Yan Zhao wrote: > > > hi Sean > > > > > > Do you think it's necessary to double check that struct page pointers > > > are also contiguous? > > > > No, the virtual address space should be irrelevant. The only way it would be > > problematic is if something in dma_map_page() expected to be able to access the > > entire chunk of memory by getting the virtual address of only the first page, > > but I can't imagine that code is reading or writing memory, let alone doing so > > across a huge range of memory. > Yes, I do find arm_iommu version of dma_map_page() access the memory by getting > virtual address of pages passed in, but it's implemented as page by page, not only > from the first page. > > dma_map_page > dma_map_page_attrs > ops->map_page > arm_iommu_map_page Heh, thankfully this is ARM specific, which presumably doesn't collide with KVMGT. > __dma_page_cpu_to_dev > dma_cache_maint_page > > Just a little worried about the condition of PFNs are contiguous > while they belong to different backends, e.g. one from system memory and > one from MMIO. > But I don't know how to avoid this without complicated checks. > And this condition might not happen in practice. IMO, assuming that contiguous pfns are vritually contiguous is wrong, i.e. would be a bug in the other code. The above dma_cache_maint_page() get's this right, and even has a well written comment to boot.
