[RFC PATCH 5/6] kvm: Re-introduce memslots->nmemslots

[Alex Williamson <alex.williamson@redhat.com>]

struct kvm_memory_slot is currently 52 bytes (LP64), not counting the
arch data.  On x86 this means the memslot array to support a tiny 32+3
entries (user+private) is over 2k.  We'd like to support more slots
so that we can support more assigned devices, but it doesn't make
sense to penalize everyone by using a statically allocated array.
This allows us to start introducing a grow-able array.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 arch/ia64/kvm/kvm-ia64.c     |    2 +-
 arch/powerpc/kvm/book3s_hv.c |    2 +-
 arch/x86/kvm/vmx.c           |    1 +
 arch/x86/kvm/x86.c           |    4 +++-
 include/linux/kvm_host.h     |    9 ++++++---
 virt/kvm/kvm_main.c          |   10 ++++++----
 6 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 012e5dd..96401b5 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1836,7 +1836,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 
 	memslot = id_to_memslot(kvm->memslots, log->slot);
 	r = -ENOENT;
-	if (!memslot->dirty_bitmap)
+	if (!memslots || !memslot->dirty_bitmap)
 		goto out;
 
 	kvm_ia64_sync_dirty_log(kvm, memslot);
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 56067db..0417190 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1267,7 +1267,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
 
 	memslot = id_to_memslot(kvm->memslots, log->slot);
 	r = -ENOENT;
-	if (!memslot->dirty_bitmap)
+	if (!memslot || !memslot->dirty_bitmap)
 		goto out;
 
 	n = kvm_dirty_bitmap_bytes(memslot);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2bb9157..07fdd90 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2751,6 +2751,7 @@ static gva_t rmode_tss_base(struct kvm *kvm)
 
 		slots = kvm_memslots(kvm);
 		slot = id_to_memslot(slots, KVM_PRIVATE_MEM_SLOTS);
+		BUG_ON(!slot);
 		base_gfn = slot->base_gfn + slot->npages - 3;
 
 		return base_gfn << PAGE_SHIFT;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8765485..53fe9b2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3139,9 +3139,11 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
 		goto out;
 
 	memslot = id_to_memslot(kvm->memslots, log->slot);
+	r = -ENOENT;
+	if (!memslot)
+		goto out;
 
 	dirty_bitmap = memslot->dirty_bitmap;
-	r = -ENOENT;
 	if (!dirty_bitmap)
 		goto out;
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7b3d5c4..1955a4e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -313,6 +313,7 @@ struct kvm_irq_routing_table {};
  * to get the memslot by its id.
  */
 struct kvm_memslots {
+	int nmemslots;
 	u64 generation;
 	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
 };
@@ -397,7 +398,7 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
 
 #define kvm_for_each_memslot(memslot, slots)	\
 	for (memslot = &slots->memslots[0];	\
-	      memslot < slots->memslots + KVM_MEM_SLOTS_NUM && memslot->npages;\
+	      memslot < slots->memslots + slots->nmemslots && memslot->npages;\
 		memslot++)
 
 int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id);
@@ -424,10 +425,12 @@ static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
 static inline struct kvm_memory_slot *
 id_to_memslot(struct kvm_memslots *slots, int id)
 {
-	int index = slots->memslots[id].id_to_index;
 	struct kvm_memory_slot *slot;
 
-	slot = &slots->memslots[index];
+	if (id >= slots->nmemslots)
+		return NULL;
+
+	slot = &slots->memslots[slots->memslots[id].id_to_index];
 
 	WARN_ON(slot->id != id);
 	return slot;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3ce2664..ebd3960 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -444,7 +444,9 @@ static void kvm_init_memslots_id(struct kvm *kvm)
 	int i;
 	struct kvm_memslots *slots = kvm->memslots;
 
-	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
+	slots->nmemslots = KVM_MEM_SLOTS_NUM;
+
+	for (i = 0; i < kvm->memslots->nmemslots; i++)
 		slots->memslots[i].id_to_index = slots->memslots[i].id = i;
 }
 
@@ -658,10 +660,10 @@ static void sort_memslots(struct kvm_memslots *slots)
 {
 	int i;
 
-	sort(slots->memslots, KVM_MEM_SLOTS_NUM,
+	sort(slots->memslots, slots->nmemslots,
 	      sizeof(struct kvm_memory_slot), cmp_memslot, NULL);
 
-	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
+	for (i = 0; i < slots->nmemslots; i++)
 		slots->memslots[slots->memslots[i].id].id_to_index = i;
 }
 
@@ -898,7 +900,7 @@ int kvm_get_dirty_log(struct kvm *kvm,
 
 	memslot = id_to_memslot(kvm->memslots, log->slot);
 	r = -ENOENT;
-	if (!memslot->dirty_bitmap)
+	if (!memslot || !memslot->dirty_bitmap)
 		goto out;
 
 	n = kvm_dirty_bitmap_bytes(memslot);