CA-381503: bump qemu filesize limit (Backport) #786
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QEMU has a file size limit to prevent denial of service attacks. However with the introduction of vTPM the vTPM state is now saved in the qemu device stream. If the vTPM happens to have a lot of data then the quota is hit, qemu returns an error, the migration fails and XAPI kills the original VM. (Same bug happens if we were trying to take a checkpoint, the VM ends up dead). Fixing that would require fast resume, which we don't have, however the file size limit needs to be updated. Don't try to be too tight on the size, the vTPM may be a max of 256KiB, so increasing this to 512KiB should work, but to be safe double that to 1MiB. Signed-off-by: Edwin Török <edwin.torok@cloud.com> Signed-off-by: Christian Lindig <christian.lindig@cloud.com>
robhoes
approved these changes
Sep 20, 2023
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Does this need to be backported? Isn't this only necessary for vTPM? |
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I asked the same question and learned that this was not just for vTPM but also emulated network drivers. |
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Is there a bug ticket for the emulated network driver issue? I don't recall seeing that. |
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In any case, backporting this change won't harm anything. |
psafont
approved these changes
Sep 21, 2023
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QEMU has a file size limit to prevent denial of service attacks. However with the introduction of vTPM the vTPM state is now saved in the qemu device stream. If the vTPM happens to have a lot of data then the quota is hit, qemu returns an error, the migration fails and XAPI kills the original VM.
(Same bug happens if we were trying to take a checkpoint, the VM ends up dead).
Fixing that would require fast resume, which we don't have, however the file size limit needs to be updated. Don't try to be too tight on the size, the vTPM may be a max of 256KiB, so increasing this to 512KiB should work, but to be safe double that to 1MiB.