powerpc/kvm/nested: Add helper to walk nested shadow linux page table.

The locking rules for walking nested shadow linux page table is different from process
scoped table. Hence add a helper for nested page table walk and also
add check whether we are holding the right locks.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200505071729.54912-11-aneesh.kumar@linux.ibm.com

arch/powerpc/kvm/book3s_hv_nested.c

@@ -750,6 +750,24 @@ static struct kvm_nested_guest *kvmhv_find_nested(struct kvm *kvm, int lpid)
 	return kvm->arch.nested_guests[lpid];
 }
 
+static pte_t *find_kvm_nested_guest_pte(struct kvm *kvm, unsigned long lpid,
+					unsigned long ea, unsigned *hshift)
+{
+	struct kvm_nested_guest *gp;
+	pte_t *pte;
+
+	gp = kvmhv_find_nested(kvm, lpid);
+	if (!gp)
+		return NULL;
+
+	VM_WARN(!spin_is_locked(&kvm->mmu_lock),
+		"%s called with kvm mmu_lock not held \n", __func__);
+	pte = __find_linux_pte(gp->shadow_pgtable, ea, NULL, hshift);
+
+	return pte;
+}
+
+
 static inline bool kvmhv_n_rmap_is_equal(u64 rmap_1, u64 rmap_2)
 {
 	return !((rmap_1 ^ rmap_2) & (RMAP_NESTED_LPID_MASK |
@@ -792,19 +810,15 @@ static void kvmhv_update_nest_rmap_rc(struct kvm *kvm, u64 n_rmap,
 				      unsigned long clr, unsigned long set,
 				      unsigned long hpa, unsigned long mask)
 {
-	struct kvm_nested_guest *gp;
 	unsigned long gpa;
 	unsigned int shift, lpid;
 	pte_t *ptep;
 
 	gpa = n_rmap & RMAP_NESTED_GPA_MASK;
 	lpid = (n_rmap & RMAP_NESTED_LPID_MASK) >> RMAP_NESTED_LPID_SHIFT;
-	gp = kvmhv_find_nested(kvm, lpid);
-	if (!gp)
-		return;
 
 	/* Find the pte */
-	ptep = __find_linux_pte(gp->shadow_pgtable, gpa, NULL, &shift);
+	ptep = find_kvm_nested_guest_pte(kvm, lpid, gpa, &shift);
 	/*
 	 * If the pte is present and the pfn is still the same, update the pte.
 	 * If the pfn has changed then this is a stale rmap entry, the nested
@@ -854,7 +868,7 @@ static void kvmhv_remove_nest_rmap(struct kvm *kvm, u64 n_rmap,
 		return;
 
 	/* Find and invalidate the pte */
-	ptep = __find_linux_pte(gp->shadow_pgtable, gpa, NULL, &shift);
+	ptep = find_kvm_nested_guest_pte(kvm, lpid, gpa, &shift);
 	/* Don't spuriously invalidate ptes if the pfn has changed */
 	if (ptep && pte_present(*ptep) && ((pte_val(*ptep) & mask) == hpa))
 		kvmppc_unmap_pte(kvm, ptep, gpa, shift, NULL, gp->shadow_lpid);
@@ -921,7 +935,7 @@ static bool kvmhv_invalidate_shadow_pte(struct kvm_vcpu *vcpu,
 	int shift;
 
 	spin_lock(&kvm->mmu_lock);
-	ptep = __find_linux_pte(gp->shadow_pgtable, gpa, NULL, &shift);
+	ptep = find_kvm_nested_guest_pte(kvm, gp->l1_lpid, gpa, &shift);
 	if (!shift)
 		shift = PAGE_SHIFT;
 	if (ptep && pte_present(*ptep)) {