Provide flexibility to the architecture to synchronize as optimally as they can instead of always taking the MMU lock for writing. Architectures that do their own locking must select CONFIG_KVM_MMU_NOTIFIER_YOUNG_LOCKLESS. The immediate application is to allow architectures to implement the test/clear_young MMU notifiers more cheaply. Suggested-by: Yu Zhao <yuzhao@xxxxxxxxxx> Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx> --- include/linux/kvm_host.h | 1 + virt/kvm/Kconfig | 3 +++ virt/kvm/kvm_main.c | 26 +++++++++++++++++++------- 3 files changed, 23 insertions(+), 7 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 692c01e41a18..4d7c3e8632e6 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -266,6 +266,7 @@ struct kvm_gfn_range { gfn_t end; union kvm_mmu_notifier_arg arg; bool may_block; + bool lockless; }; bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range); bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range); diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig index 29b73eedfe74..0404857c1702 100644 --- a/virt/kvm/Kconfig +++ b/virt/kvm/Kconfig @@ -97,6 +97,9 @@ config KVM_GENERIC_MMU_NOTIFIER select MMU_NOTIFIER bool +config KVM_MMU_NOTIFIER_YOUNG_LOCKLESS + bool + config KVM_GENERIC_MEMORY_ATTRIBUTES depends on KVM_GENERIC_MMU_NOTIFIER bool diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 14841acb8b95..d8fa0d617f12 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -558,6 +558,7 @@ struct kvm_mmu_notifier_range { on_lock_fn_t on_lock; bool flush_on_ret; bool may_block; + bool lockless; }; /* @@ -612,6 +613,10 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, IS_KVM_NULL_FN(range->handler))) return r; + /* on_lock will never be called for lockless walks */ + if (WARN_ON_ONCE(range->lockless && !IS_KVM_NULL_FN(range->on_lock))) + return r; + idx = srcu_read_lock(&kvm->srcu); for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) { @@ -643,15 +648,18 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, gfn_range.start = hva_to_gfn_memslot(hva_start, slot); gfn_range.end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, slot); gfn_range.slot = slot; + gfn_range.lockless = range->lockless; if (!r.found_memslot) { r.found_memslot = true; - KVM_MMU_LOCK(kvm); - if (!IS_KVM_NULL_FN(range->on_lock)) - range->on_lock(kvm); - - if (IS_KVM_NULL_FN(range->handler)) - break; + if (!range->lockless) { + KVM_MMU_LOCK(kvm); + if (!IS_KVM_NULL_FN(range->on_lock)) + range->on_lock(kvm); + + if (IS_KVM_NULL_FN(range->handler)) + break; + } } r.ret |= range->handler(kvm, &gfn_range); } @@ -660,7 +668,7 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, if (range->flush_on_ret && r.ret) kvm_flush_remote_tlbs(kvm); - if (r.found_memslot) + if (r.found_memslot && !range->lockless) KVM_MMU_UNLOCK(kvm); srcu_read_unlock(&kvm->srcu, idx); @@ -681,6 +689,8 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .on_lock = (void *)kvm_null_fn, .flush_on_ret = true, .may_block = false, + .lockless = + IS_ENABLED(CONFIG_KVM_MMU_NOTIFIER_YOUNG_LOCKLESS), }; return __kvm_handle_hva_range(kvm, &range).ret; @@ -699,6 +709,8 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .on_lock = (void *)kvm_null_fn, .flush_on_ret = false, .may_block = false, + .lockless = + IS_ENABLED(CONFIG_KVM_MMU_NOTIFIER_YOUNG_LOCKLESS), }; return __kvm_handle_hva_range(kvm, &range).ret; -- 2.45.2.505.gda0bf45e8d-goog