KVM: Do not restrict the size of KVM-internal memory regions

Exempt KVM-internal memslots from the KVM_MEM_MAX_NR_PAGES restriction, as
the limit on the number of pages exists purely to play nice with dirty
bitmap operations, which use 32-bit values to index the bitmaps, and dirty
logging isn't supported for KVM-internal memslots.

Link: https://lore.kernel.org/all/20240802205003.353672-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20250123144627.312456-2-imbrenda@linux.ibm.com
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20250123144627.312456-2-imbrenda@linux.ibm.com>

Author: sean-jc

virt/kvm/kvm_main.c

@@ -1971,7 +1971,15 @@ static int kvm_set_memory_region(struct kvm *kvm,
 		return -EINVAL;
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
 		return -EINVAL;
-	if ((mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
+
+	/*
+	 * The size of userspace-defined memory regions is restricted in order
+	 * to play nice with dirty bitmap operations, which are indexed with an
+	 * "unsigned int".  KVM's internal memory regions don't support dirty
+	 * logging, and so are exempt.
+	 */
+	if (id < KVM_USER_MEM_SLOTS &&
+	    (mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
 		return -EINVAL;
 
 	slots = __kvm_memslots(kvm, as_id);