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 --- tools/testing/selftests/kvm/clear_dirty_log_test.c | 2 ++ 1 file changed, 2 insertions(+) create mode 100644 tools/testing/selftests/kvm/clear_dirty_log_test.c (limited to 'tools/testing/selftests/kvm/clear_dirty_log_test.c') 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" -- cgit v1.2.3-59-g8ed1b