> privately-managed pages into a sparse vm area with the following steps:
>
> area = get_vm_area(area_size, VM_SPARSE); // at bpf prog verification time
> vm_area_map_pages(area, kaddr, 1, page); // on demand
> // it will return an error if kaddr is out of range
> vm_area_unmap_pages(area, kaddr, 1);
> free_vm_area(area); // after bpf prog is unloaded
I'm still wondering if this should just use an opaque cookie instead
of exposing the vm_area. But otherwise this mostly looks fine to me.
> + if (addr < (unsigned long)area->addr || (void *)end > area->addr + area->size)
> + return -ERANGE;
This check is duplicated so many times that it really begs for a helper.
> +int vm_area_unmap_pages(struct vm_struct *area, unsigned long addr, unsigned int count)
> +{
> + unsigned long size = ((unsigned long)count) * PAGE_SIZE;
> + unsigned long end = addr + size;
> +
> + if (WARN_ON_ONCE(!(area->flags & VM_SPARSE)))
> + return -EINVAL;
> + if (addr < (unsigned long)area->addr || (void *)end > area->addr + area->size)
> + return -ERANGE;
> +
> + vunmap_range(addr, end);
> + return 0;
Does it make much sense to have an error return here vs just debug
checks? It's not like the caller can do much if it violates these
basic invariants.
