[Expired for QEMU because there has been no activity for 60 days.]
** Changed in: qemu
Status: Incomplete => Expired
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https://bugs.launchpad.net/bugs/1497479
Title:
memory corruption with migrate/savevm in TCG mode
Status in QEMU:
Expired
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 always hit by a running VM code during the execution of the
`ram_save_iterate' by migration thread then these pages are missing in the
dirty log. The TLB is always hit for instance when the VM is mostly idling and
the Kernel only handles APIC timer interrupts.
3. These pages are then missed during `ram_save_complete' stage.
4. This makes memory content in a saved VM state differ from the actual VM
memory.
5. If the affected memory pages contain some Kernel data structures these can
be corrupted by this memory inconsistency, causing 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
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