KVM: MMU: fix missing locking in alloc_mmu_pages

n_requested_mmu_pages/n_free_mmu_pages are used by
kvm_mmu_change_mmu_pages to calculate the number of pages to zap.

alloc_mmu_pages, called from the vcpu initialization path, modifies this
variables without proper locking, which can result in a negative value
in kvm_mmu_change_mmu_pages (say, with cpu hotplug).

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 87c67f449279..86c2551fe136 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2728,12 +2728,14 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
 
         ASSERT(vcpu);
 
+        spin_lock(&vcpu->kvm->mmu_lock);
         if (vcpu->kvm->arch.n_requested_mmu_pages)
                 vcpu->kvm->arch.n_free_mmu_pages =
                                         vcpu->kvm->arch.n_requested_mmu_pages;
         else
                 vcpu->kvm->arch.n_free_mmu_pages =
                                         vcpu->kvm->arch.n_alloc_mmu_pages;
+        spin_unlock(&vcpu->kvm->mmu_lock);
         /*
          * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
          * Therefore we need to allocate shadow page tables in the first