[edk2-devel] Does EDK2 ArmVirtPkg has support for a virtio-mmio-blk device

[Ying Fang]

On 2021/2/10 2:32 上午, Laszlo Ersek wrote:
> On 02/09/21 16:28, Ard Biesheuvel wrote:
>> On Tue, 9 Feb 2021 at 14:41, Laszlo Ersek <lersek at redhat.com> wrote:
>>>
>>> On 02/09/21 03:54, Ying Fang wrote:
>>>
>>>> I now realize that we emulate the virtio-blk-device over mmio, and we
>>>> only emulate virtio-1.0 spec.
>>>> As mentioned in (1c) , EDK2 only supports virtio-0.95 spec for now, so
>>>> this maybe a big problem.
>>>> Since it may not handshake ok if we only emulate virtio-1.0.
>>>
>>> Yes.
>>>
>>> First, the MMIO transport (as I remember from checking it last time,
>>> which was quite some time ago) is very different between 0.9.5 and 1.0.
>>>
>>> Second, device initialization steps differ:
>>> - between 0.9.5 MMIO and 0.9.5 PCI,
>>> - between 0.9.5 and 1.0, regardless of transport.
>>>
>>> This means that the device driver code has *some* specifics (=
>>> abstraction leaks) that relate to the underlying transport (MMIO vs.
>>> PCI, and 0.9.5 vs. 1.0). See:
>>>
>>> OvmfPkg/VirtioBlkDxe/VirtioBlk.c
>>>
>>> 752 //
>>> 753 // Set Page Size - MMIO VirtIo Specific
>>> 754 //
>>> 755 Status = Dev->VirtIo->SetPageSize (Dev->VirtIo, EFI_PAGE_SIZE);
>>>
>>> 822 //
>>> 823 // In virtio-1.0, feature negotiation is expected to complete before queue
>>> 824 // discovery, and the device can also reject the selected set of features.
>>> 825 //
>>> 826 if (Dev->VirtIo->Revision >= VIRTIO_SPEC_REVISION (1, 0, 0)) {
>>> 827 Status = Virtio10WriteFeatures (Dev->VirtIo, Features, &NextDevStat);
>>>
>>> 867 //
>>> 868 // Additional steps for MMIO: align the queue appropriately, and set the
>>> 869 // size. If anything fails from here on, we must unmap the ring resources.
>>> 870 //
>>> 871 Status = Dev->VirtIo->SetQueueNum (Dev->VirtIo, QueueSize);
>>>
>>> 894 //
>>> 895 // step 5 -- Report understood features.
>>> 896 //
>>> 897 if (Dev->VirtIo->Revision < VIRTIO_SPEC_REVISION (1, 0, 0)) {
>>> 898 Features &= ~(UINT64)(VIRTIO_F_VERSION_1 | VIRTIO_F_IOMMU_PLATFORM);
>>> 899 Status = Dev->VirtIo->SetGuestFeatures (Dev->VirtIo, Features);
>>>
>>> We tried to make these "abstraction leaks" as small as possible; for
>>> example the MMIO specific operations (SetPageSize, SetQueueNum) are
>>> performed unconditionally, and it's only the PCI transport backends that
>>> simply ignore those actions (after performing some sanity checks).
>>> However, the different order of initialization steps couldn't really be
>>> hidden (I wasn't comfortable with simply regression-testing the new 1.0
>>> order against 0.9.5 transports of QEMU, so we kept both init orders).
>>>
>>> Virtio MMIO was always classified as "temporary" and "legacy", needed
>>> only until PCI support would be brought about on ARM. So given the
>>> increased complexity of Virtio MMIO in the 1.0 spec, I always believed
>>> that designing and implementing the latter in OVMF would be a waste of
>>> effort.

Agreed, for most use cases we should first implement PCI stuff before
using EDK2 on ARM platform.

For now we are building StratoVirt [1] (a light weight VMM) using Rust
language just like firecracker does.

Futher we are planing to bring EDK2 boot and ACPI features for it.
However the PCI feature is WIP, so we are using Virtio MMIO as a
temporary approach. We will switch to PCI when the PCI feature is done,
so it won't be a problem. I am just trying to test the EDK2
functionality using ArmVirtPkg QEMU desgin before PCI support.

[1] https://gitee.com/openeuler/stratovirt

>>>
>>>
>>>> I will try to emulate the virtio-0.95 later to see if it is the root
>>>> cause.
>>>
>>> Yes, please either do that, or please add a PCI host.
>>>
>>> Given that you do get a BLK0: alias in the UEFI shell, the
>>> initialization of the device might even *appear* to complete, to OVMF;
>>> however, the actual virtio transfers likely fail.
>>>
>>
>> That BLK0: alias in the UEFI shell is the NOR flash not a virtio block device.

Thanks for pointing it out. I was once recognizing it as the Virtio
Block device by mistake.

>>
>
> Sigh, thanks.
>
> In the original message, only "VenHw(xxx, 00)" was included, and I
> couldn't tell at once whether the vendor GUID was indeed
> gVirtioMmioTransportGuid (837DCA9E-E874-4D82-B29A-23FE0E23D1E2). So I
> assumed. :/
>
> Ying Fang: in the future, please only paste actual logs. If you edit the
> log, you may render it useless. In this instance, you managed to edit
> out a relatively important log detail.

Thanks, I will follow your guide.

>
> Thanks, Ard!
> Laszlo
>
>

Many Thanks.
Ying Fang.

>
> 
>



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