On Fri, May 24, 2024 at 08:40:26AM +0000, Tian, Kevin wrote: > > From: Peter Xu <peterx@xxxxxxxxxx> > > Sent: Friday, May 24, 2024 8:49 AM > > > > Hi, Yan, > > > > On Fri, May 24, 2024 at 08:39:37AM +0800, Yan Zhao wrote: > > > On Thu, May 23, 2024 at 01:56:27PM -0600, Alex Williamson wrote: > > > > With the vfio device fd tied to the address space of the pseudo fs > > > > inode, we can use the mm to track all vmas that might be mmap'ing > > > > device BARs, which removes our vma_list and all the complicated lock > > > > ordering necessary to manually zap each related vma. > > > > > > > > Note that we can no longer store the pfn in vm_pgoff if we want to use > > > > unmap_mapping_range() to zap a selective portion of the device fd > > > > corresponding to BAR mappings. > > > > > > > > This also converts our mmap fault handler to use vmf_insert_pfn() > > > Looks vmf_insert_pfn() does not call memtype_reserve() to reserve > > memory type > > > for the PFN on x86 as what's done in io_remap_pfn_range(). > > > > > > Instead, it just calls lookup_memtype() and determine the final prot based > > on > > > the result from this lookup, which might not prevent others from reserving > > the > > > PFN to other memory types. > > > > I didn't worry too much on others reserving the same pfn range, as that > > should be the mmio region for this device, and this device should be owned > > by vfio driver. > > and the earliest point doing memtype_reserve() is here: > > vfio_pci_core_mmap() > vdev->barmap[index] = pci_iomap(pdev, index, 0); > > > > > However I share the same question, see: > > > > https://lore.kernel.org/r/20240523223745.395337-2-peterx@xxxxxxxxxx > > > > So far I think it's not a major issue as VFIO always use UC- mem type, and > > that's also the default. But I do also feel like there's something we can > > do better, and I'll keep you copied too if I'll resend the series. > > > > vfio-nvgrace uses WC. But it directly does remap_pfn_range() in its > nvgrace_gpu_mmap() so not suffering from the issue here. People keep asking for WC on normal VFIO PCI as well, we shouldn't rule out, or at least provide a big warning comment what needs to be fixed to allow it. Jason
