summaryrefslogtreecommitdiffstats
path: root/arch/x86
diff options
context:
space:
mode:
authorTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>2012-08-20 18:35:39 +0900
committerAvi Kivity <avi@redhat.com>2012-08-22 15:27:13 +0300
commit35f2d16bb9ace0fb2671b8232839944ad9057c6f (patch)
tree763610b668cb62664b55a838488e96dad829a9b0 /arch/x86
parente8143ccb6b501f78bb95d9c5ee100d18423008cf (diff)
downloadlinux-35f2d16bb9ace0fb2671b8232839944ad9057c6f.tar.bz2
KVM: MMU: Fix mmu_shrink() so that it can free mmu pages as intended
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>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kvm/mmu.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 01ca00423938..7fbd0d273ea8 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4113,16 +4113,21 @@ static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
LIST_HEAD(invalid_list);
/*
+ * Never scan more than sc->nr_to_scan VM instances.
+ * Will not hit this condition practically since we do not try
+ * to shrink more than one VM and it is very unlikely to see
+ * !n_used_mmu_pages so many times.
+ */
+ if (!nr_to_scan--)
+ break;
+ /*
* n_used_mmu_pages is accessed without holding kvm->mmu_lock
* here. We may skip a VM instance errorneosly, but we do not
* want to shrink a VM that only started to populate its MMU
* anyway.
*/
- if (kvm->arch.n_used_mmu_pages > 0) {
- if (!nr_to_scan--)
- break;
+ if (!kvm->arch.n_used_mmu_pages)
continue;
- }
idx = srcu_read_lock(&kvm->srcu);
spin_lock(&kvm->mmu_lock);