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David Alan Gilbert" , peterx@redhat.com, Fabiano Rosas Subject: [PATCH v2 09/13] migration/postcopy: Initialize blocktime context only until listen Date: Mon, 9 Jun 2025 15:12:55 -0400 Message-ID: <20250609191259.9053-10-peterx@redhat.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250609191259.9053-1-peterx@redhat.com> References: <20250609191259.9053-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Before this patch, the blocktime context can be created very early, because postcopy_ram_supported_by_host() <- migrate_caps_check() can happen during migration object init. The trick here is the blocktime context needs system vCPU information, which seems to be possible to change after that point. I didn't verify it, but it doesn't sound right. Now move it out and initialize the context only when postcopy listen starts. That is already during a migration so it should be guaranteed the vCPU topology can never change on both sides. While at it, assert that the ctx isn't created instead this time; the old "if" trick isn't needed when we're sure it will only happen once now. Reviewed-by: Fabiano Rosas Signed-off-by: Peter Xu --- migration/postcopy-ram.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c index 98d4c29532..6ed4546744 100644 --- a/migration/postcopy-ram.c +++ b/migration/postcopy-ram.c @@ -324,13 +324,13 @@ static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis, } #ifdef UFFD_FEATURE_THREAD_ID + /* + * Postcopy blocktime conditionally needs THREAD_ID feature (introduced + * to Linux in 2017). Always try to enable it when QEMU is compiled + * with such environment. + */ if (UFFD_FEATURE_THREAD_ID & supported_features) { asked_features |= UFFD_FEATURE_THREAD_ID; - if (migrate_postcopy_blocktime()) { - if (!mis->blocktime_ctx) { - mis->blocktime_ctx = blocktime_context_new(); - } - } } #endif @@ -1238,6 +1238,11 @@ int postcopy_ram_incoming_setup(MigrationIncomingState *mis) return -1; } + if (migrate_postcopy_blocktime()) { + assert(mis->blocktime_ctx == NULL); + mis->blocktime_ctx = blocktime_context_new(); + } + /* Now an eventfd we use to tell the fault-thread to quit */ mis->userfault_event_fd = eventfd(0, EFD_CLOEXEC); if (mis->userfault_event_fd == -1) { -- 2.49.0