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/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>
Reviewed-by: Christoph Schlameuss <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Claudio Imbrenda <[email protected]>
Message-ID: <[email protected]>

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);