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author | Paolo Bonzini <pbonzini@redhat.com> | 2018-10-23 02:36:47 +0200 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2018-12-14 12:34:19 +0100 |
commit | 2a31b9db153530df4aa02dac8c32837bf5f47019 (patch) | |
tree | 0cd6fe156ec696e6a55a0d7117794f590ec76958 /include/linux/kvm_host.h | |
parent | 8fe65a8299f9e1f40cb95308ab7b3c4ad80bf801 (diff) | |
download | linux-2a31b9db153530df4aa02dac8c32837bf5f47019.tar.gz linux-2a31b9db153530df4aa02dac8c32837bf5f47019.tar.bz2 linux-2a31b9db153530df4aa02dac8c32837bf5f47019.zip |
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 <pbonzini@redhat.com>
Diffstat (limited to 'include/linux/kvm_host.h')
-rw-r--r-- | include/linux/kvm_host.h | 5 |
1 files changed, 5 insertions, 0 deletions
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); |