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authorPaolo Bonzini2018-10-23 02:36:47 +0200
committerPaolo Bonzini2018-12-14 12:34:19 +0100
commit2a31b9db153530df4aa02dac8c32837bf5f47019 (patch)
tree0cd6fe156ec696e6a55a0d7117794f590ec76958 /include/uapi/linux/kvm.h
parentkvm: rename last argument to kvm_get_dirty_log_protect (diff)
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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/uapi/linux/kvm.h')
-rw-r--r--include/uapi/linux/kvm.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2b7a652c9fa4..9fe35f1ac938 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -492,6 +492,17 @@ struct kvm_dirty_log {
};
};
+/* for KVM_CLEAR_DIRTY_LOG */
+struct kvm_clear_dirty_log {
+ __u32 slot;
+ __u32 num_pages;
+ __u64 first_page;
+ union {
+ void __user *dirty_bitmap; /* one bit per page */
+ __u64 padding2;
+ };
+};
+
/* for KVM_SET_SIGNAL_MASK */
struct kvm_signal_mask {
__u32 len;
@@ -975,6 +986,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_HYPERV_ENLIGHTENED_VMCS 163
#define KVM_CAP_EXCEPTION_PAYLOAD 164
#define KVM_CAP_ARM_VM_IPA_SIZE 165
+#define KVM_CAP_MANUAL_DIRTY_LOG_PROTECT 166
#ifdef KVM_CAP_IRQ_ROUTING
@@ -1421,6 +1433,9 @@ struct kvm_enc_region {
#define KVM_GET_NESTED_STATE _IOWR(KVMIO, 0xbe, struct kvm_nested_state)
#define KVM_SET_NESTED_STATE _IOW(KVMIO, 0xbf, struct kvm_nested_state)
+/* Available with KVM_CAP_MANUAL_DIRTY_LOG_PROTECT */
+#define KVM_CLEAR_DIRTY_LOG _IOWR(KVMIO, 0xc0, struct kvm_clear_dirty_log)
+
/* Secure Encrypted Virtualization command */
enum sev_cmd_id {
/* Guest initialization commands */