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authorPaolo Bonzini2021-08-03 03:45:41 -0400
committerPaolo Bonzini2021-08-03 03:54:08 -0400
commit071064f14d87536e38235df1bdeabe404023203f (patch)
treebe48cfdff46fbaedb60513a0049d1b49f2c328ce
parent52ac8b358b0cb7e91c966225fca61be5d1c984bc (diff)
KVM: Don't take mmu_lock for range invalidation unless necessary
Avoid taking mmu_lock for .invalidate_range_{start,end}() notifications that are unrelated to KVM. This is possible now that memslot updates are blocked from range_start() to range_end(); that ensures that lock elision happens in both or none, and therefore that mmu_notifier_count updates (which must occur while holding mmu_lock for write) are always paired across start->end. Based on patches originally written by Ben Gardon. Signed-off-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--virt/kvm/kvm_main.c25
1 files changed, 12 insertions, 13 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8f9024d65866..930aeb8d3c3e 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -496,17 +496,6 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
idx = srcu_read_lock(&kvm->srcu);
- /* The on_lock() path does not yet support lock elision. */
- if (!IS_KVM_NULL_FN(range->on_lock)) {
- locked = true;
- KVM_MMU_LOCK(kvm);
-
- range->on_lock(kvm, range->start, range->end);
-
- if (IS_KVM_NULL_FN(range->handler))
- goto out_unlock;
- }
-
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
kvm_for_each_memslot(slot, slots) {
@@ -538,6 +527,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
if (!locked) {
locked = true;
KVM_MMU_LOCK(kvm);
+ if (!IS_KVM_NULL_FN(range->on_lock))
+ range->on_lock(kvm, range->start, range->end);
+ if (IS_KVM_NULL_FN(range->handler))
+ break;
}
ret |= range->handler(kvm, &gfn_range);
}
@@ -546,7 +539,6 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
if (range->flush_on_ret && (ret || kvm->tlbs_dirty))
kvm_flush_remote_tlbs(kvm);
-out_unlock:
if (locked)
KVM_MMU_UNLOCK(kvm);
@@ -605,8 +597,14 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
/*
* .change_pte() must be surrounded by .invalidate_range_{start,end}().
+ * If mmu_notifier_count is zero, then no in-progress invalidations,
+ * including this one, found a relevant memslot at start(); rechecking
+ * memslots here is unnecessary. Note, a false positive (count elevated
+ * by a different invalidation) is sub-optimal but functionally ok.
*/
WARN_ON_ONCE(!READ_ONCE(kvm->mn_active_invalidate_count));
+ if (!READ_ONCE(kvm->mmu_notifier_count))
+ return;
kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
}
@@ -1398,7 +1396,8 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
/*
* Do not store the new memslots while there are invalidations in
- * progress (preparatory change for the next commit).
+ * progress, otherwise the locking in invalidate_range_start and
+ * invalidate_range_end will be unbalanced.
*/
spin_lock(&kvm->mn_invalidate_lock);
prepare_to_rcuwait(&kvm->mn_memslots_update_rcuwait);