KVM: mmu_shrink: kvm_mmu_zap_page requires slots_lock to be held

kvm_mmu_zap_page() needs slots lock held (rmap_remove->gfn_to_memslot,
for example).

Since kvm_lock spinlock is held in mmu_shrink(), do a non-blocking
down_read_trylock().

Untested.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1fd8e3b58cc0..ff7cf632175b 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1987,6 +1987,8 @@ static int mmu_shrink(int nr_to_scan, gfp_t gfp_mask)
         list_for_each_entry(kvm, &vm_list, vm_list) {
                 int npages;
 
+                if (!down_read_trylock(&kvm->slots_lock))
+                        continue;
                 spin_lock(&kvm->mmu_lock);
                 npages = kvm->arch.n_alloc_mmu_pages -
                          kvm->arch.n_free_mmu_pages;
@@ -1999,6 +2001,7 @@ static int mmu_shrink(int nr_to_scan, gfp_t gfp_mask)
                 nr_to_scan--;
 
                 spin_unlock(&kvm->mmu_lock);
+                up_read(&kvm->slots_lock);
         }
         if (kvm_freed)
                 list_move_tail(&kvm_freed->vm_list, &vm_list);