static ssize_t debugfs_radix_read()

in kvm/book3s_64_mmu_radix.c [1288:1438]

• 142 lines of code
• 27 McCabe index (conditional complexity)

static ssize_t debugfs_radix_read(struct file *file, char __user *buf,
				 size_t len, loff_t *ppos)
{
	struct debugfs_radix_state *p = file->private_data;
	ssize_t ret, r;
	unsigned long n;
	struct kvm *kvm;
	unsigned long gpa;
	pgd_t *pgt;
	struct kvm_nested_guest *nested;
	pgd_t *pgdp;
	p4d_t p4d, *p4dp;
	pud_t pud, *pudp;
	pmd_t pmd, *pmdp;
	pte_t *ptep;
	int shift;
	unsigned long pte;

	kvm = p->kvm;
	if (!kvm_is_radix(kvm))
		return 0;

	ret = mutex_lock_interruptible(&p->mutex);
	if (ret)
		return ret;

	if (p->chars_left) {
		n = p->chars_left;
		if (n > len)
			n = len;
		r = copy_to_user(buf, p->buf + p->buf_index, n);
		n -= r;
		p->chars_left -= n;
		p->buf_index += n;
		buf += n;
		len -= n;
		ret = n;
		if (r) {
			if (!n)
				ret = -EFAULT;
			goto out;
		}
	}

	gpa = p->gpa;
	nested = NULL;
	pgt = NULL;
	while (len != 0 && p->lpid >= 0) {
		if (gpa >= RADIX_PGTABLE_RANGE) {
			gpa = 0;
			pgt = NULL;
			if (nested) {
				kvmhv_put_nested(nested);
				nested = NULL;
			}
			p->lpid = kvmhv_nested_next_lpid(kvm, p->lpid);
			p->hdr = 0;
			if (p->lpid < 0)
				break;
		}
		if (!pgt) {
			if (p->lpid == 0) {
				pgt = kvm->arch.pgtable;
			} else {
				nested = kvmhv_get_nested(kvm, p->lpid, false);
				if (!nested) {
					gpa = RADIX_PGTABLE_RANGE;
					continue;
				}
				pgt = nested->shadow_pgtable;
			}
		}
		n = 0;
		if (!p->hdr) {
			if (p->lpid > 0)
				n = scnprintf(p->buf, sizeof(p->buf),
					      "\nNested LPID %d: ", p->lpid);
			n += scnprintf(p->buf + n, sizeof(p->buf) - n,
				      "pgdir: %lx\n", (unsigned long)pgt);
			p->hdr = 1;
			goto copy;
		}

		pgdp = pgt + pgd_index(gpa);
		p4dp = p4d_offset(pgdp, gpa);
		p4d = READ_ONCE(*p4dp);
		if (!(p4d_val(p4d) & _PAGE_PRESENT)) {
			gpa = (gpa & P4D_MASK) + P4D_SIZE;
			continue;
		}

		pudp = pud_offset(&p4d, gpa);
		pud = READ_ONCE(*pudp);
		if (!(pud_val(pud) & _PAGE_PRESENT)) {
			gpa = (gpa & PUD_MASK) + PUD_SIZE;
			continue;
		}
		if (pud_val(pud) & _PAGE_PTE) {
			pte = pud_val(pud);
			shift = PUD_SHIFT;
			goto leaf;
		}

		pmdp = pmd_offset(&pud, gpa);
		pmd = READ_ONCE(*pmdp);
		if (!(pmd_val(pmd) & _PAGE_PRESENT)) {
			gpa = (gpa & PMD_MASK) + PMD_SIZE;
			continue;
		}
		if (pmd_val(pmd) & _PAGE_PTE) {
			pte = pmd_val(pmd);
			shift = PMD_SHIFT;
			goto leaf;
		}

		ptep = pte_offset_kernel(&pmd, gpa);
		pte = pte_val(READ_ONCE(*ptep));
		if (!(pte & _PAGE_PRESENT)) {
			gpa += PAGE_SIZE;
			continue;
		}
		shift = PAGE_SHIFT;
	leaf:
		n = scnprintf(p->buf, sizeof(p->buf),
			      " %lx: %lx %d\n", gpa, pte, shift);
		gpa += 1ul << shift;
	copy:
		p->chars_left = n;
		if (n > len)
			n = len;
		r = copy_to_user(buf, p->buf, n);
		n -= r;
		p->chars_left -= n;
		p->buf_index = n;
		buf += n;
		len -= n;
		ret += n;
		if (r) {
			if (!ret)
				ret = -EFAULT;
			break;
		}
	}
	p->gpa = gpa;
	if (nested)
		kvmhv_put_nested(nested);

 out:
	mutex_unlock(&p->mutex);
	return ret;
}