Its a long shot since its still asmedia, but I was hoping the chipset groupings were improved.
So far on the taichi b550 the whole chipset is one iommu group …
@wendell, on the ASRock Taichi and MSI Carbon B550 reviews that you’ve done so far, you have stated that you do do not recommend B550 for VFIO passthrough because all of the functionality tied to the ASMedia chipset is all in a single IOMMU group. But is this really the death knell for VFIO passthrough gaming on the B550? Don’t we still have the opportunity to passthrough everything that a VFIO gaming VM still needs?
The following links confirm what you said about the chipset IOMMU group, but I think that they also show that the non-chipset stuff can still be passed through:
The non-ASMedia device interfaces includes:
PCIe 4.0 x16 or x8+x8 (GPU) slots
PCIe 4.0x4 M.2
USB 3.2
USB 2.0
Audio Device
That seems to be everything a gaming VM might want passthrough access to, other than a dedicated Ethernet device (I was planning on using a network bridge). So, assuming that the VM doesn’t need the second (slow) M.2, the (slower) SATA drives, the remaining PCIe3.0 x1 slot, or all of the other USB devices, is this still no longer good for an IOMMU gaming rig?
I feel like either 1) i am missing something obvious that will cause my B550 virtualized gaming dreams to crumble away, or 2) your IOMMU recommendation was dependent on criteria of being able to passthrough devices tied to the chipset, because X570 can do that extra bit.
Please let me know your thoughts on this particular usage case, as I would love to know whether or not my B550 dreams can still be realized.
thanks for any insight you can provide.
I mentioned that in the videos. You could but if the price of x570 is about the same, why? To avoid fan whine?
Generally I also want to run my host on the fastest storage but would concede that m.2 pcie3 for the host wouldn’t be super terrible.
I am not sure about the stability of native USB passthrough. I seem to have better luck passing through the entire pcie device for pcieusb adapters on the south bridge, if I even pass through a USB controller. A lot of the time I don’t anymore.
I have a MSI B550 ITX board but I have not installed it yet as waiting on NVMe stuff to turn up from the flooded lands. 
The layout looks functionally the same as B450 at the end of the day. You can use that for passthrough generally because as you’ve seen there are enough items that are separated to get the job done.
I was hoping it would be closer to the x570 situation combined with a bit better power consumption (x570 sucks up about twice as much at idle as x470) but I’m not surprised its no better.
The worst parts are: B550 isn’t really any cheaper than x570 in general and 8x/8x split while technically supported basically doesn’t exist outside of $250+ boards on x570 or b550. In fact, a lot of these boards only have 2x or even 1x actual lanes connected to their secondary 16x slots! I actually bought a x470 once I realized this as the new chipsets are inferior for vfio purposes unless I want to double my motherboard budget.
I have an MSI Mag B550 Tomahawk. The primary gpu slot is isolated but that is it unfortunately.
Pretty much this.
I mean why even bother with B550 for this kind of use case scenario´s?
It’s not like that B550 board prices are that interesting either.
A good B550 board with a reasonable set of connectivity features,
and a good vrm starts at around the $180,- ish price mark.
And at this point you could very well just pick a decent X570 board instead really.
Then i´m not even going to start talking about the physical,
limitation of B550 in general at this point.
So yeah indeed why bother…? 
I mean there are really cool and good B550 boards around.
But they are just not really that great or interesting,
for these kind of workloads.
I have the MSI B550 ITX one, not sure on IOMMU groups yet, I don’t have a APU for this thing yet so haven’t really looked into it.
Hopeful the 5000 series APU’s will be more interesting then the 4000 series (which are marketed for OEM and laptop mostly).
Maybe one day we will get WSL2 in reverse so windows10 can run in a sub-system on Linux and all this VM stuff won’t be needed. 
So… as I consider to pick up a ASRock B550M for my miniITX build, it’s kinda okay if all I want to passthrough is the dedicated graphics card, a USB controller and a M.2 drive? 
The USB controller might be a problem as I believe will be connected to the chipset, which puts all devices in one iommu group.
That sounds bad.
Or is this ACS patch helping here in anyway?
I never applied it and albeit having fear from setting up libvirt, things were pretty smooth on my openSuSE system with its B450 mainboard
ACS patch may help separate the devices, though I have read it can cause stability issues on some systems. Worth a try, but B550 so far isn’t great for passthrough.
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Interesting.
Under these circumstances, maybe I just leave the system on native Windows too.
Thanks for replying to my questions, I have to see what I am going to do now
I ended up holding off on B550…
While fan whine is irritating, the real problem with the chipset fan is that it increases the likelihood of unrecoverable failure during my expected period of ownership of at least 5 years. This is past the warranty of most MBs, and while I’m sure that they would love for me to just purchase a newer one, I’d rather avoid replacement until i have sufficiently updated computational needs.
This ended up being the real concern for me. I had planned on trying a single-gpu VFIO system, but if @wendell says that native USB passthrough might be a problem, then it is dead to me.
With an ATX-sized fully passive X570 solution announced, I think that I have finally settled on the solution for me.
With Ryzen, there is a single USB controller that is part of the CPU. That is typically in its own IOMMU group and can be passed through, although I think Zen2 had some issues with it combined with earlier linux kernels, not sure.
One other reason that x570 isn’t great is it uses over twice as much power at idle as x470 and presumably b550. debau8er tested it. For the most part its the better rough for vfio though.