On Thu, May 18, 2023 at 11:04:46AM -0700, Sean Christopherson wrote: > 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.
Actually, this is fine with KVMGT (owning to page by page access), isn't it? :) > > > __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. Right.
