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 --- virt/kvm/arm/arm.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'virt/kvm/arm/arm.c') diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index 120a2663dab9..e91adf77d99a 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -1219,6 +1219,22 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log) return r; } +int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm, struct kvm_clear_dirty_log *log) +{ + bool flush = false; + int r; + + mutex_lock(&kvm->slots_lock); + + r = kvm_clear_dirty_log_protect(kvm, log, &flush); + + if (flush) + kvm_flush_remote_tlbs(kvm); + + mutex_unlock(&kvm->slots_lock); + return r; +} + static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm, struct kvm_arm_device_addr *dev_addr) { -- cgit