kvm: mmu: Fix overflow on kvm mmu page limit calculation

KVM bases its memory usage limits on the total number of guest pages
across all memslots. However, those limits, and the calculations to
produce them, use 32 bit unsigned integers. This can result in overflow
if a VM has more guest pages that can be represented by a u32. As a
result of this overflow, KVM can use a low limit on the number of MMU
pages it will allocate. This makes KVM unable to map all of guest memory
at once, prompting spurious faults.

Tested: Ran all kvm-unit-tests on an Intel Haswell machine. This patch
	introduced no new failures.

Signed-off-by: Ben Gardon <bgardon@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 099b851dabaf..455f156f56ed 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4270,7 +4270,7 @@ static int kvm_vm_ioctl_set_identity_map_addr(struct kvm *kvm,
 }
 
 static int kvm_vm_ioctl_set_nr_mmu_pages(struct kvm *kvm,
-					  u32 kvm_nr_mmu_pages)
+					 unsigned long kvm_nr_mmu_pages)
 {
 	if (kvm_nr_mmu_pages < KVM_MIN_ALLOC_MMU_PAGES)
 		return -EINVAL;
@@ -4284,7 +4284,7 @@ static int kvm_vm_ioctl_set_nr_mmu_pages(struct kvm *kvm,
 	return 0;
 }
 
-static int kvm_vm_ioctl_get_nr_mmu_pages(struct kvm *kvm)
+static unsigned long kvm_vm_ioctl_get_nr_mmu_pages(struct kvm *kvm)
 {
 	return kvm->arch.n_max_mmu_pages;
 }