[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v3 0/4] virtio-iommu: Support VIRTIO_IOMMU_F_BYPASS_CONFIG
From: |
Eric Auger |
Subject: |
Re: [PATCH v3 0/4] virtio-iommu: Support VIRTIO_IOMMU_F_BYPASS_CONFIG |
Date: |
Tue, 15 Feb 2022 10:16:40 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 |
Hi Connie,
On 2/14/22 6:34 PM, Cornelia Huck wrote:
> On Mon, Feb 14 2022, Jean-Philippe Brucker <jean-philippe@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-philippe@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.
>
- [PATCH v3 0/4] virtio-iommu: Support VIRTIO_IOMMU_F_BYPASS_CONFIG, Jean-Philippe Brucker, 2022/02/14
- [PATCH v3 2/4] virtio-iommu: Default to bypass during boot, Jean-Philippe Brucker, 2022/02/14
- [PATCH v3 1/4] linux-headers: update to v5.17-rc1, Jean-Philippe Brucker, 2022/02/14
- [PATCH v3 4/4] tests/qtest/virtio-iommu-test: Check bypass config, Jean-Philippe Brucker, 2022/02/14
- [PATCH v3 3/4] virtio-iommu: Support bypass domain, Jean-Philippe Brucker, 2022/02/14
- Re: [PATCH v3 0/4] virtio-iommu: Support VIRTIO_IOMMU_F_BYPASS_CONFIG, Cornelia Huck, 2022/02/14
- Re: [PATCH v3 0/4] virtio-iommu: Support VIRTIO_IOMMU_F_BYPASS_CONFIG,
Eric Auger <=
- Re: [PATCH v3 0/4] virtio-iommu: Support VIRTIO_IOMMU_F_BYPASS_CONFIG, Eric Auger, 2022/02/15