On Tue, Apr 09, 2024 at 04:45:22PM +0000, Zeng, Oak wrote: > > I saw, I am saying this should not be done. You cannot unmap bits of > > a sgl mapping if an invalidation comes in. > > You are right, if we register a huge mmu interval notifier to cover > the whole address space, then we should use dma map/unmap pages to > map bits of the address space. We will explore this approach. > > Right now, in xe driver, mmu interval notifier is dynamically > registered with small address range. We map/unmap the whole small > address ranges each time. So functionally it still works. But it > might not be as performant as the method you said. Please don't do this, it is not how hmm_range_fault() should be used. It is intended to be page by page and there is no API surface available to safely try to construct covering ranges. Drivers definately should not try to invent such a thing. > > Please don't use sg list at all for this. > > As explained, we use sg list for device private pages so we can > re-used the gpu page table update codes. I'm asking you not to use SGL lists for that too. SGL lists are not generic data structures to hold DMA lists. > > This is not what I'm talking about. The GPU VMA is bound to a specific > > MM VA, it should not be created on demand. > > Today we have two places where we create gpu vma: 1) create gpu vma > during a vm_bind ioctl 2) create gpu vma during a page fault of the > system allocator range (this will be in v2 of this series). Don't do 2. > I suspect something dynamic is still necessary, either a vma or a > page table state (1 vma but many page table state created > dynamically, as planned in our stage 2). I'm expecting you'd populate the page table memory on demand. > The reason is, we still need some gpu corresponding structure to > match the cpu vm_area_struct. Definately not. > For example, when gpu page fault happens, you look > up the cpu vm_area_struct for the fault address and create a > corresponding state/struct. And people can have as many cpu > vm_area_struct as they want. No you don't. You call hmm_range_fault() and it does everything for you. A driver should never touch CPU VMAs and must not be aware of them in any away. Jason
