On Thu, Oct 8, 2020 at 2:44 AM John Hubbard <jhubb...@nvidia.com> wrote: > > On 10/7/20 9:44 AM, Daniel Vetter wrote: > > Way back it was a reasonable assumptions that iomem mappings never > > change the pfn range they point at. But this has changed: > > > > - gpu drivers dynamically manage their memory nowadays, invalidating > > ptes with unmap_mapping_range when buffers get moved > > > > - contiguous dma allocations have moved from dedicated carvetouts to > > s/carvetouts/carveouts/ > > > cma regions. This means if we miss the unmap the pfn might contain > > pagecache or anon memory (well anything allocated with GFP_MOVEABLE) > > > > - even /dev/mem now invalidates mappings when the kernel requests that > > iomem region when CONFIG_IO_STRICT_DEVMEM is set, see 3234ac664a87 > > ("/dev/mem: Revoke mappings when a driver claims the region") > > Thanks for putting these references into the log, it's very helpful. > ... > > diff --git a/mm/memory.c b/mm/memory.c > > index fcfc4ca36eba..8d467e23b44e 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -4873,28 +4873,68 @@ int follow_phys(struct vm_area_struct *vma, > > return ret; > > } > > > > +/** > > + * generic_access_phys - generic implementation for iomem mmap access > > + * @vma: the vma to access > > + * @addr: userspace addres, not relative offset within @vma > > + * @buf: buffer to read/write > > + * @len: length of transfer > > + * @write: set to FOLL_WRITE when writing, otherwise reading > > + * > > + * This is a generic implementation for &vm_operations_struct.access for an > > + * iomem mapping. This callback is used by access_process_vm() when the > > @vma is > > + * not page based. > > + */ > > int generic_access_phys(struct vm_area_struct *vma, unsigned long addr, > > void *buf, int len, int write) > > { > > resource_size_t phys_addr; > > unsigned long prot = 0; > > void __iomem *maddr; > > + pte_t *ptep, pte; > > + spinlock_t *ptl; > > int offset = addr & (PAGE_SIZE-1); > > + int ret = -EINVAL; > > + > > + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) > > + return -EINVAL; > > + > > +retry: > > + if (follow_pte(vma->vm_mm, addr, &ptep, &ptl)) > > + return -EINVAL; > > + pte = *ptep; > > + pte_unmap_unlock(ptep, ptl); > > > > - if (follow_phys(vma, addr, write, &prot, &phys_addr)) > > + prot = pgprot_val(pte_pgprot(pte)); > > + phys_addr = (resource_size_t)pte_pfn(pte) << PAGE_SHIFT; > > + > > + if ((write & FOLL_WRITE) && !pte_write(pte)) > > return -EINVAL; > > > > maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), prot); > > if (!maddr) > > return -ENOMEM; > > > > + if (follow_pte(vma->vm_mm, addr, &ptep, &ptl)) > > + goto out_unmap; > > + > > + if (pte_same(pte, *ptep)) { > > > The ioremap area is something I'm sorta new to, so a newbie question: > is it possible for the same pte to already be there, ever? If so, we > be stuck in an infinite loop here. I'm sure that's not the case, but > it's not yet obvious to me why it's impossible. Resource reservations > maybe?
It's just buggy, it should be !pte_same. And I need to figure out how to test this I guess. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel