Public bug reported: [ISSUE]
QEMU releases 2.3.1 and lower are forgetting to flush TLBs before enabling the global dirty pages log and entering the final stage of saving the VM. [DESCRIPTION] The situation is the following: 1. TLB misses is the only way for page dirtying in the TCG mode. 2. If TLB is hit by a running VM during the execution of the `ram_save_iterate' by migration thread (e.g. if VM is mostly idling) then some pages are missing in the dirty log. 3. These pages are then not migrated during `ram_save_complete'. 4. This makes memory content in a saved VM state differ from the actual VM memory. 5. If the affected area includes some Kernel data structures such as trees or lists this can cause Kernel to Oops after loading the saved state. [SOLUTION] A proposed solution is to flush TLB when `log_global_start' is called. Here is the patch: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1493049/+attachment/4459905/+files/tcg-commit-on-log-global-start.patch [LINKS] Ubuntu bug: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1493049 ** Affects: qemu Importance: Undecided Status: New -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1497479 Title: memory corruption with migrate/savevm in TCG mode Status in QEMU: New Bug description: [ISSUE] QEMU releases 2.3.1 and lower are forgetting to flush TLBs before enabling the global dirty pages log and entering the final stage of saving the VM. [DESCRIPTION] The situation is the following: 1. TLB misses is the only way for page dirtying in the TCG mode. 2. If TLB is hit by a running VM during the execution of the `ram_save_iterate' by migration thread (e.g. if VM is mostly idling) then some pages are missing in the dirty log. 3. These pages are then not migrated during `ram_save_complete'. 4. This makes memory content in a saved VM state differ from the actual VM memory. 5. If the affected area includes some Kernel data structures such as trees or lists this can cause Kernel to Oops after loading the saved state. [SOLUTION] A proposed solution is to flush TLB when `log_global_start' is called. Here is the patch: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1493049/+attachment/4459905/+files/tcg-commit-on-log-global-start.patch [LINKS] Ubuntu bug: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1493049 To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1497479/+subscriptions