From 2a31b9db153530df4aa02dac8c32837bf5f47019 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 23 Oct 2018 02:36:47 +0200 Subject: kvm: introduce manual dirty log reprotect There are two problems with KVM_GET_DIRTY_LOG. First, and less important, it can take kvm->mmu_lock for an extended period of time. Second, its user can actually see many false positives in some cases. The latter is due to a benign race like this: 1. KVM_GET_DIRTY_LOG returns a set of dirty pages and write protects them. 2. The guest modifies the pages, causing them to be marked ditry. 3. Userspace actually copies the pages. 4. KVM_GET_DIRTY_LOG returns those pages as dirty again, even though they were not written to since (3). This is especially a problem for large guests, where the time between (1) and (3) can be substantial. This patch introduces a new capability which, when enabled, makes KVM_GET_DIRTY_LOG not write-protect the pages it returns. Instead, userspace has to explicitly clear the dirty log bits just before using the content of the page. The new KVM_CLEAR_DIRTY_LOG ioctl can also operate on a 64-page granularity rather than requiring to sync a full memslot; this way, the mmu_lock is taken for small amounts of time, and only a small amount of time will pass between write protection of pages and the sending of their content. Signed-off-by: Paolo Bonzini --- include/linux/kvm_host.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux/kvm_host.h') diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 8c56b2873b13..e065aeaae29e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -449,6 +449,7 @@ struct kvm { #endif long tlbs_dirty; struct list_head devices; + bool manual_dirty_log_protect; struct dentry *debugfs_dentry; struct kvm_stat_data **debugfs_stat_data; struct srcu_struct srcu; @@ -754,6 +755,8 @@ int kvm_get_dirty_log(struct kvm *kvm, int kvm_get_dirty_log_protect(struct kvm *kvm, struct kvm_dirty_log *log, bool *flush); +int kvm_clear_dirty_log_protect(struct kvm *kvm, + struct kvm_clear_dirty_log *log, bool *flush); void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm, struct kvm_memory_slot *slot, @@ -762,6 +765,8 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm, int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log); +int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm, + struct kvm_clear_dirty_log *log); int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level, bool line_status); -- cgit