[vfio-users] [FEEDBACK NEEDED] Additionnal tips to include in the Arch wiki article

[Spam House]

Hey Colin,

I am curious about this as well. Please provide more information on your
setup regarding X2APIC.

On Sat, May 21, 2016 at 10:42 AM, Colin Godsey <crgodsey at gmail.com> wrote:

> Windows 10 forcing X2APIC: https://support.microsoft.com/en-us/kb/2303458
>
> This helped a bunch for me at least on 4.4- I think there was some
> confusion on the correct way to signal the guest on what APIC to use,
> forcing this gave me much better %sys times. AFAIK it can also still be
> used with hyper-v APIC because that’s just the EOI para-virtualization.
>
> On Fri, May 20, 2016 at 2:28 PM Alex Williamson <
> alex.l.williamson at gmail.com> wrote:
>
>> On Fri, May 20, 2016 at 11:38 AM, Nicolas Roy-Renaud <
>> nicolas.roy-renaud.1 at ens.etsmtl.ca> wrote:
>>
>>> Did you have any issues with efifb or some other driver grabbing the
>>> gard before vfio-pci? What are your IOMMU groups like, which chard is your
>>> boot_vga, what script or method do you use to get vfio-pci to bind with
>>> your card, what's your kernel command line and what modules are included in
>>> your initramfs?
>>>
>>> I've struggled with getting my primary GPU to work correctly for a
>>> passthrough like this, and I ended up switching it up with the secondary
>>> because I simply couldn't get it to work properly (I'd keep getting
>>> something about "Invalid ROM contents") and I couldn't see my boot logs
>>> until the host driver finished loading. It's really inconvenient now
>>> becuase my motherboard is designed so that having a full-size GPU in the
>>> second PCIe slot blocks 4 SATA ports out of 6, so I need to have L-shaped
>>> cables in a bunch of places to make everything work properly.
>>>
>>
>> The boot VGA ROM is handled differently from other PCI ROMs in Linux,
>> when you read it you're actually reading a shadow copy of it placed at
>> 0xc0000, which has its roots back in the original IBM PC history.
>> Execution of the VGA ROM is allowed to modify this copy of the ROM image in
>> memory.  Thus you're really not getting a pristine copy of the device ROM
>> and it can often lead to these invalid ROM contents messages.  I wish we
>> provided raw access to the PCI option ROM in these cases as well.  For now,
>> if you do have these sorts of invalid ROM messages, I would suggest that
>> you at least boot with the card as secondary, dump the ROM, then use that
>> collected image with the romfile= option rather than use the shadow copy.
>> I had to add some code to vfio to fix device IDs and checksums for IGD
>> assignment because of this, I don't know if there's any standard fixup we
>> can do for other vendors.  Thanks,
>>
>> Alex
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>
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