Although the possible race described in
commit 85b7059169e128c57a3a8a3e588fb89cb2031da1
KVM: MMU: fix shrinking page from the empty mmu
was correct, the real cause of that issue was a more trivial bug of
mmu_shrink() introduced by
commit 1952639665e92481c34c34c3e2a71bf3e66ba362
KVM: MMU: do not iterate over all VMs in mmu_shrink()
Here is the bug:
if (kvm->arch.n_used_mmu_pages > 0) {
if (!nr_to_scan--)
break;
continue;
}
We skip VMs whose n_used_mmu_pages is not zero and try to shrink others:
in other words we try to shrink empty ones by mistake.
This patch reverses the logic so that mmu_shrink() can free pages from
the first VM whose n_used_mmu_pages is not zero. Note that we also add
comments explaining the role of nr_to_scan which is not practically
important now, hoping this will be improved in the future.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Cc: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
35f2d16bb9