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authorPaolo Bonzini <pbonzini@redhat.com>2018-10-23 02:36:47 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2018-12-14 12:34:19 +0100
commit2a31b9db153530df4aa02dac8c32837bf5f47019 (patch)
tree0cd6fe156ec696e6a55a0d7117794f590ec76958 /tools/testing/selftests/kvm/clear_dirty_log_test.c
parentkvm: rename last argument to kvm_get_dirty_log_protect (diff)
downloadlinux-dev-2a31b9db153530df4aa02dac8c32837bf5f47019.tar.xz
linux-dev-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 'tools/testing/selftests/kvm/clear_dirty_log_test.c')
-rw-r--r--tools/testing/selftests/kvm/clear_dirty_log_test.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/tools/testing/selftests/kvm/clear_dirty_log_test.c b/tools/testing/selftests/kvm/clear_dirty_log_test.c
new file mode 100644
index 000000000000..749336937d37
--- /dev/null
+++ b/tools/testing/selftests/kvm/clear_dirty_log_test.c
@@ -0,0 +1,2 @@
+#define USE_CLEAR_DIRTY_LOG
+#include "dirty_log_test.c"