On Tue, Feb 15 2022, Jean-Philippe Brucker <jean-phili...@linaro.org> wrote:
> On Tue, Feb 15, 2022 at 10:16:40AM +0100, Eric Auger wrote: >> 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. > > I agree, it seems too unlikely that someone would want to migrate it back > to 6.2 where it wasn't really useable except for experiments Fair enough. Let's make this an Acked-by: Cornelia Huck <coh...@redhat.com> (for the series)
