int kvm_arch_prepare_memory_region()

in kvm/mmu.c [444:538]

• 58 lines of code
• 15 McCabe index (conditional complexity)

int kvm_arch_prepare_memory_region(struct kvm *kvm,
				const struct kvm_memory_slot *old,
				struct kvm_memory_slot *new,
				enum kvm_mr_change change)
{
	hva_t hva, reg_end, size;
	gpa_t base_gpa;
	bool writable;
	int ret = 0;

	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
			change != KVM_MR_FLAGS_ONLY)
		return 0;

	/*
	 * Prevent userspace from creating a memory region outside of the GPA
	 * space addressable by the KVM guest GPA space.
	 */
	if ((new->base_gfn + new->npages) >=
	    (stage2_gpa_size >> PAGE_SHIFT))
		return -EFAULT;

	hva = new->userspace_addr;
	size = new->npages << PAGE_SHIFT;
	reg_end = hva + size;
	base_gpa = new->base_gfn << PAGE_SHIFT;
	writable = !(new->flags & KVM_MEM_READONLY);

	mmap_read_lock(current->mm);

	/*
	 * A memory region could potentially cover multiple VMAs, and
	 * any holes between them, so iterate over all of them to find
	 * out if we can map any of them right now.
	 *
	 *     +--------------------------------------------+
	 * +---------------+----------------+   +----------------+
	 * |   : VMA 1     |      VMA 2     |   |    VMA 3  :    |
	 * +---------------+----------------+   +----------------+
	 *     |               memory region                |
	 *     +--------------------------------------------+
	 */
	do {
		struct vm_area_struct *vma = find_vma(current->mm, hva);
		hva_t vm_start, vm_end;

		if (!vma || vma->vm_start >= reg_end)
			break;

		/*
		 * Mapping a read-only VMA is only allowed if the
		 * memory region is configured as read-only.
		 */
		if (writable && !(vma->vm_flags & VM_WRITE)) {
			ret = -EPERM;
			break;
		}

		/* Take the intersection of this VMA with the memory region */
		vm_start = max(hva, vma->vm_start);
		vm_end = min(reg_end, vma->vm_end);

		if (vma->vm_flags & VM_PFNMAP) {
			gpa_t gpa = base_gpa + (vm_start - hva);
			phys_addr_t pa;

			pa = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
			pa += vm_start - vma->vm_start;

			/* IO region dirty page logging not allowed */
			if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
				ret = -EINVAL;
				goto out;
			}

			ret = stage2_ioremap(kvm, gpa, pa,
					     vm_end - vm_start, writable);
			if (ret)
				break;
		}
		hva = vm_end;
	} while (hva < reg_end);

	if (change == KVM_MR_FLAGS_ONLY)
		goto out;

	spin_lock(&kvm->mmu_lock);
	if (ret)
		stage2_unmap_range(kvm, base_gpa, size, false);
	spin_unlock(&kvm->mmu_lock);

out:
	mmap_read_unlock(current->mm);
	return ret;
}