[RFC KVM 12/27] kvm/isolation: add KVM page table entry allocation functions

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

These functions allocate p4d/pud/pmd/pte pages and ensure that
pages are in the KVM page table.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
 arch/x86/kvm/isolation.c |   94 ++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 94 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/isolation.c b/arch/x86/kvm/isolation.c
index b29a09b..6ec86df 100644
--- a/arch/x86/kvm/isolation.c
+++ b/arch/x86/kvm/isolation.c
@@ -248,6 +248,100 @@ static inline void kvm_p4d_free(struct mm_struct *mm, p4d_t *p4d)
 	p4d_free(mm, PGTD_ALIGN(p4d));
 }
 
+/*
+ * kvm_pXX_alloc() functions are equivalent to kernel pXX_alloc()
+ * 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_alloc(struct mm_struct *mm, pmd_t *pmd,
+			    unsigned long addr)
+{
+	pte_t *pte;
+
+	if (pmd_none(*pmd)) {
+		pte = pte_alloc_kernel(pmd, addr);
+		if (!pte) {
+			pr_debug("PTE: ERR ALLOC\n");
+			return ERR_PTR(-ENOMEM);
+		}
+		if (!kvm_add_pgt_directory(pte, PGT_LEVEL_PTE)) {
+			kvm_pte_free(mm, pte);
+			return ERR_PTR(-EINVAL);
+		}
+	} else {
+		pte = kvm_pte_offset(pmd, addr);
+	}
+
+	return pte;
+}
+
+static pmd_t *kvm_pmd_alloc(struct mm_struct *mm, pud_t *pud,
+			    unsigned long addr)
+{
+	pmd_t *pmd;
+
+	if (pud_none(*pud)) {
+		pmd = pmd_alloc(mm, pud, addr);
+		if (!pmd) {
+			pr_debug("PMD: ERR ALLOC\n");
+			return ERR_PTR(-ENOMEM);
+		}
+		if (!kvm_add_pgt_directory(pmd, PGT_LEVEL_PMD)) {
+			kvm_pmd_free(mm, pmd);
+			return ERR_PTR(-EINVAL);
+		}
+	} else {
+		pmd = kvm_pmd_offset(pud, addr);
+	}
+
+	return pmd;
+}
+
+static pud_t *kvm_pud_alloc(struct mm_struct *mm, p4d_t *p4d,
+			    unsigned long addr)
+{
+	pud_t *pud;
+
+	if (p4d_none(*p4d)) {
+		pud = pud_alloc(mm, p4d, addr);
+		if (!pud) {
+			pr_debug("PUD: ERR ALLOC\n");
+			return ERR_PTR(-ENOMEM);
+		}
+		if (!kvm_add_pgt_directory(pud, PGT_LEVEL_PUD)) {
+			kvm_pud_free(mm, pud);
+			return ERR_PTR(-EINVAL);
+		}
+	} else {
+		pud = kvm_pud_offset(p4d, addr);
+	}
+
+	return pud;
+}
+
+static p4d_t *kvm_p4d_alloc(struct mm_struct *mm, pgd_t *pgd,
+			    unsigned long addr)
+{
+	p4d_t *p4d;
+
+	if (pgd_none(*pgd)) {
+		p4d = p4d_alloc(mm, pgd, addr);
+		if (!p4d) {
+			pr_debug("P4D: ERR ALLOC\n");
+			return ERR_PTR(-ENOMEM);
+		}
+		if (!kvm_add_pgt_directory(p4d, PGT_LEVEL_P4D)) {
+			kvm_p4d_free(mm, p4d);
+			return ERR_PTR(-EINVAL);
+		}
+	} else {
+		p4d = kvm_p4d_offset(pgd, addr);
+	}
+
+	return p4d;
+}
+
 
 static int kvm_isolation_init_mm(void)
 {
-- 
1.7.1