[RFC KVM 11/27] kvm/isolation: add KVM page table entry offset functions

[Alexandre Chartre <alexandre.chartre@oracle.com>]

These functions are wrappers are the p4d/pud/pmd/pte offset functions
which ensure that page table pointers are in the KVM page table.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
 arch/x86/kvm/isolation.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 61 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/isolation.c b/arch/x86/kvm/isolation.c
index 61df750..b29a09b 100644
--- a/arch/x86/kvm/isolation.c
+++ b/arch/x86/kvm/isolation.c
@@ -162,6 +162,67 @@ static bool kvm_valid_pgt_entry(void *ptr)
 }
 
 /*
+ * kvm_pXX_offset() functions are equivalent to kernel pXX_offset()
+ * functions but, in addition, they ensure that page table pointers
+ * are in the KVM page table. Otherwise an error is returned.
+ */
+
+static pte_t *kvm_pte_offset(pmd_t *pmd, unsigned long addr)
+{
+	pte_t *pte;
+
+	pte = pte_offset_map(pmd, addr);
+	if (!kvm_valid_pgt_entry(pte)) {
+		pr_err("PTE %px is not in KVM page table\n", pte);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return pte;
+}
+
+static pmd_t *kvm_pmd_offset(pud_t *pud, unsigned long addr)
+{
+	pmd_t *pmd;
+
+	pmd = pmd_offset(pud, addr);
+	if (!kvm_valid_pgt_entry(pmd)) {
+		pr_err("PMD %px is not in KVM page table\n", pmd);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return pmd;
+}
+
+static pud_t *kvm_pud_offset(p4d_t *p4d, unsigned long addr)
+{
+	pud_t *pud;
+
+	pud = pud_offset(p4d, addr);
+	if (!kvm_valid_pgt_entry(pud)) {
+		pr_err("PUD %px is not in KVM page table\n", pud);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return pud;
+}
+
+static p4d_t *kvm_p4d_offset(pgd_t *pgd, unsigned long addr)
+{
+	p4d_t *p4d;
+
+	p4d = p4d_offset(pgd, addr);
+	/*
+	 * p4d is the same has pgd if we don't have a 5-level page table.
+	 */
+	if ((p4d != (p4d_t *)pgd) && !kvm_valid_pgt_entry(p4d)) {
+		pr_err("P4D %px is not in KVM page table\n", p4d);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return p4d;
+}
+
+/*
  * kvm_pXX_free() functions are equivalent to kernel pXX_free()
  * functions but they can be used with any PXX pointer in the
  * directory.
-- 
1.7.1