KVM: PPC: Book3S Nested: Use explicit 4096 LPID maximum

Rather than tie this to KVMPPC_NR_LPIDS which is becoming more dynamic,
fix it to 4096 (12-bits) explicitly for now.

kvmhv_get_nested() does not have to check against KVM_MAX_NESTED_GUESTS
because the L1 partition table registration hcall already did that, and
it checks against the partition table size.

This patch also puts all the partition table size calculations into the
same form, using 12 for the architected size field shift and 4 for the
shift corresponding to the partition table entry size.
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-of-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220123120043.3586018-6-npiggin@gmail.com

arch/powerpc/include/asm/kvm_host.h

@@ -36,7 +36,12 @@
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 #include <asm/kvm_book3s_asm.h>		/* for MAX_SMT_THREADS */
 #define KVM_MAX_VCPU_IDS	(MAX_SMT_THREADS * KVM_MAX_VCORES)
-#define KVM_MAX_NESTED_GUESTS	KVMPPC_NR_LPIDS
+
+/*
+ * Limit the nested partition table to 4096 entries (because that's what
+ * hardware supports). Both guest and host use this value.
+ */
+#define KVM_MAX_NESTED_GUESTS_SHIFT	12
 
 #else
 #define KVM_MAX_VCPU_IDS	KVM_MAX_VCPUS

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -266,7 +266,7 @@ int kvmppc_mmu_hv_init(void)
 			return -EINVAL;
 		nr_lpids = 1UL << mmu_lpid_bits;
 	} else {
-		nr_lpids = KVM_MAX_NESTED_GUESTS;
+		nr_lpids = 1UL << KVM_MAX_NESTED_GUESTS_SHIFT;
 	}
 
 	if (nr_lpids > KVMPPC_NR_LPIDS)

arch/powerpc/kvm/book3s_hv_nested.c

@@ -439,10 +439,11 @@ long kvmhv_nested_init(void)
 	if (!radix_enabled())
 		return -ENODEV;
 
-	/* find log base 2 of KVMPPC_NR_LPIDS, rounding up */
-	ptb_order = __ilog2(KVMPPC_NR_LPIDS - 1) + 1;
-	if (ptb_order < 8)
-		ptb_order = 8;
+	/* Partition table entry is 1<<4 bytes in size, hence the 4. */
+	ptb_order = KVM_MAX_NESTED_GUESTS_SHIFT + 4;
+	/* Minimum partition table size is 1<<12 bytes */
+	if (ptb_order < 12)
+		ptb_order = 12;
 	pseries_partition_tb = kmalloc(sizeof(struct patb_entry) << ptb_order,
 				       GFP_KERNEL);
 	if (!pseries_partition_tb) {
@@ -450,7 +451,7 @@ long kvmhv_nested_init(void)
 		return -ENOMEM;
 	}
 
-	ptcr = __pa(pseries_partition_tb) | (ptb_order - 8);
+	ptcr = __pa(pseries_partition_tb) | (ptb_order - 12);
 	rc = plpar_hcall_norets(H_SET_PARTITION_TABLE, ptcr);
 	if (rc != H_SUCCESS) {
 		pr_err("kvm-hv: Parent hypervisor does not support nesting (rc=%ld)\n",
@@ -534,16 +535,14 @@ long kvmhv_set_partition_table(struct kvm_vcpu *vcpu)
 	long ret = H_SUCCESS;
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
-	/*
-	 * Limit the partition table to 4096 entries (because that's what
-	 * hardware supports), and check the base address.
-	 */
-	if ((ptcr & PRTS_MASK) > 12 - 8 ||
+	/* Check partition size and base address. */
+	if ((ptcr & PRTS_MASK) + 12 - 4 > KVM_MAX_NESTED_GUESTS_SHIFT ||
 	    !kvm_is_visible_gfn(vcpu->kvm, (ptcr & PRTB_MASK) >> PAGE_SHIFT))
 		ret = H_PARAMETER;
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 	if (ret == H_SUCCESS)
 		kvm->arch.l1_ptcr = ptcr;
+
 	return ret;
 }
 
@@ -639,7 +638,7 @@ static void kvmhv_update_ptbl_cache(struct kvm_nested_guest *gp)
 
 	ret = -EFAULT;
 	ptbl_addr = (kvm->arch.l1_ptcr & PRTB_MASK) + (gp->l1_lpid << 4);
-	if (gp->l1_lpid < (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 8))) {
+	if (gp->l1_lpid < (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 12 - 4))) {
 		int srcu_idx = srcu_read_lock(&kvm->srcu);
 		ret = kvm_read_guest(kvm, ptbl_addr,
 				     &ptbl_entry, sizeof(ptbl_entry));
@@ -809,8 +808,7 @@ struct kvm_nested_guest *kvmhv_get_nested(struct kvm *kvm, int l1_lpid,
 {
 	struct kvm_nested_guest *gp, *newgp;
 
-	if (l1_lpid >= KVM_MAX_NESTED_GUESTS ||
-	    l1_lpid >= (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 12 - 4)))
+	if (l1_lpid >= (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 12 - 4)))
 		return NULL;
 
 	spin_lock(&kvm->mmu_lock);