Hi Connie, On 2/14/22 6:34 PM, Cornelia Huck wrote: > On Mon, Feb 14 2022, Jean-Philippe Brucker <jean-phili...@linaro.org> wrote: > >> Replace the VIRTIO_IOMMU_F_BYPASS feature with >> VIRTIO_IOMMU_F_BYPASS_CONFIG, which enables a config space bit to switch >> global bypass on and off. >> >> Add a boot-bypass option, which defaults to 'on' to be in line with >> other vIOMMUs and to allow running firmware/bootloader that are unaware >> of the IOMMU. x86 doesn't need a workaround to boot with virtio-iommu >> anymore. >> >> Since v2 [1]: >> * Added the new bypass bits to the migration stream. >> As discussed on the v2 thread, we assume that cross-version >> compatibility is not required for live migration at the moment, so we >> only increase the version number. Patch 2 says: "We add the bypass >> field to the migration stream without introducing subsections, based >> on the assumption that this virtio-iommu device isn't being used in >> production enough to require cross-version migration at the moment >> (all previous version required workarounds since they didn't support >> ACPI and boot-bypass)." >> >> [1] >> https://lore.kernel.org/qemu-devel/20220127142940.671333-1-jean-phili...@linaro.org/ > One thing that we could do to avoid surprises in the unlikely case that > somebody has a virtio-iommu device and wants to migrate to an older > machine version is to add a migration blocker for the virtio-iommu > device for all compat machines for versions 6.2 or older (i.e. only 7.0 > or newer machine types can have a migratable virtio-iommu device > starting with QEMU 7.0.) Not too complicated to implement, but I'm not > sure whether we'd add too much code to prevent something very unlikely > to happen anyway. I would not insist on it :) As nobody has shout and we are not aware of anybody using the device in production mode yet due to the missing boot bypass feature this series brings, I would be personally in favour of leaving things as is. Now, up to Jean if he wants to go and implement your suggestion.
Thanks Eric > > Otherwise, I didn't spot problems in this series. >
